Hi Marko, that isn’t one of my videos you referred to, so I can’t really answer you properly as I don’t know how their track was created. For the best answer, you should really contact the video creator. There isn’t any research that I’ve seen to suggest that you could harm your health by looping a delta track. During a typical sleep cycle, your brainwave activity will usually go up and down between the delta and theta range. It may be that you won’t experience the same quality of sleep if you spend most of your time producing mainly delta activity. With my 8-hour sleep track, I fluctuate the frequency range to try and emulate a typical sleep cycle http://www.mindamend.com/shop/sleeping-and-dreaming/deep-sleep-8-hour-sleep-cycle/.
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It may be that you had the volume too loud, but I would expect you to hear the effects of that straight after you’ve stopped listening, not on a day you haven’t used them. It might be something similar to muscle memory, where you suddenly remembered the sound and sensations it gives you as if you were hearing it again. I don’t know how long you’ve been using this type of thing for, but maybe it’s something that will settle down and disappear once you become more accustomed to the sound.
Above is a nice, simple and short chart of the various brainwave ranges and the types of effects they generally have and what sorts of activities they may be able to enhance. There simply is nothing more detailed than what this chart contains about entrainment frequencies and what they are useful for. Those other elaborate lists to be found on the internet are nothing but the product of overactive imaginations.
These two tracks entrain the brain to specific frequencies in the lower regions of Beta brainwaves, beneath 20 Hertz. Most people are operating in a stressful brainwave frequency above 20Hz during their days, so listening to these tracks while you work, commute, run errands or anything else during your waking day will help you maintain a calm, yet active state of mind.
We are all unique and herbs can work differently for different people. The usage instructions on the label are written to be applicable to a general population. However, that doesn't mean they are optimum for you and the discomforts you are experiencing (small vs. large body types for example). "As needed" means you should take the amount listed at a needed frequency until you feel the desired effect (paying attention to any maximum or frequency limitations listed).

Delta is the lowest frequency range of .2Hz - 3Hz, corresponding to dreamless sleep, growth hormone release, healing and ultra deep trance. Effective in reducing migraines, chronic pain and blood pressure. By inducing a predominantly Delta state in the brain while remaining awake, you push your brain to operate in a truly unique state that literally forces greater neural adaptation and cross-connection between the regions of your brain.

If you’re going to enter a state of meditation, a technique of some sort must be employed that takes you there. (Note – I am fully aware of references to “spontaneous enlightenment experiences”, but these are an entirely different category of phenomena than what is being discussed here and are outside the scope of this discussion. Perhaps another time.)
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Theta brain waves occur most often in sleep but are also dominant in deep meditation. Theta is known to be a dreamlike state with vivid imagery, intuition and information beyond your normal conscious awareness. This state of mind is excellent for psychic experiences to occur, as well as astral projection and extended remote viewing. To reach this state without falling asleep while meditating takes practice.
“The great neuroscientist W. Gray Walter carried out a series of experiments in the late forties and fifties in which he used an electronic stroboscopic device in combination with EEG equipment to send rhythmic light flashes into the eyes of the subjects at frequencies ranging from ten to twenty five flashes per second. He was startled to find that the flickering seemed to alter the brain-wave activity of the whole cortex instead of just the areas associated with vision. Wrote Walter, “The rhythmic series of flashes appear to be breaking down some of the physiologic barriers between different regions of the brain. This means the stimulus of flicker received by the visual projection area of the cortex was breaking bounds— its ripples were overflowing into other areas.”

While binaural beats are the most common technique we use for producing brainwave entrainment music, we do use other brainwave entrainment techniques such as isochronic tones, monaural beats and amplitude modulation. If these techniques have been used then you will find them mentioned in the written description of the music productions that include them. If not mentioned, then you can assume that binaural beats are the only brainwave entrainment technology in use.
A binaureal beat is created by playing a different tone in each ear, and the interference pattern between the slightly differing frequencies creates the illusion of a beat. It's intended to be heard through headphones, so there's no cross-channel bleed across both ears. Listen to this, I'll play a simple binaural beat, and I'll slide the pan control back and forth from one ear to the other. You can see that there isn't actually any beat, it's just an acoustic illusion:
Binaural beats were discovered in 1839 by a German experimenter, H. W. Dove. The human ability to "hear" binaural beats appears to be the result of evolutionary adaptation. Many evolved species can detect binaural beats because of their brain structure. The frequencies at which binaural beats can be detected change depending upon the size of the species' cranium. In the human, binaural beats can be detected when carrier waves are below approximately 1000 Hz (Oster, 1973). Below 1000 Hz the wave length of the signal is longer than the diameter of the human skull. Thus, signals below 1000 Hz curve around the skull by diffraction. The same effect can be observed with radio wave propagation. Lower-frequency (longer wave length) radio waves (such as AM radio) travel around the earth over and in between mountains and structures. Higher-frequency (shorter wave length) radio waves (such as FM radio, TV, and microwaves) travel in a straight line and can't curve around the earth. Mountains and structures block these high-frequency signals. Because frequencies below 1000 Hz curve around the skull, incoming signals below 1000 Hz are heard by both ears. But due to the distance between the ears, the brain "hears" the inputs from the ears as out of phase with each other. As the sound wave passes around the skull, each ear gets a different portion of the wave. It is this waveform phase difference that allows for accurate location of sounds below 1000 Hz(9). Audio direction finding at higher frequencies is less accurate than it is for frequencies below 1000 Hz. At 8000 Hz the pinna (external ear) becomes effective as an aid to localization. In summary it's the ability of the brain to detect a waveform phase difference is what enables it to perceive binaural beats.
Entrainment is a phenomenon seen is a wide variety of different natural circumstance. In the field of chronobiology, the study of biological rhythms in living organisms, entrainment is the synchronization of a circadian rhythm with the rhythm of an external pattern, such as the synchronizing of women’s menstrual cycles with the phases of the moon or with one another in a group.
Effects on cortisol: The hormone cortisol is commonly associated with stress, and when levels are higher than usual, it can have a negative impact on the body. High levels of cortisol can lead to a range of conditions, including Cushing syndrome, menstrual cycle and female libido changes, anxiety, and depression. Dr. Giampapa noted a reduction of cortisol of up to 70-80 percent in several study participants.
Words could be great stress relievers. One technique to quell sudden stress is to repeat a phrase from which you draw power and strength. “Think positively about releasing what is bothering you by repeating a positive mantra that uplifts you such as, ‘I am at peace,’ ‘All is well,’ ‘I choose to think thoughts that serve me,’ or ‘I love and believe in myself fully,’” says Carol Whitaker, life transformation expert and the author of Ridiculously Happy! The Secret to Manifesting the Life and Body of Your Dreams. “This too shall pass” is another good one. Repeating a mantra is actually a type of meditation that can make you more resilient to stress—some studies show it can actually alter your brain’s neural pathways. You can place reminders of your mantras near the places you tend to get stressed, like your work space. “I actually keep a file on my computer of great quotes and inspiring sayings. So when I’m feeling overwhelmed by life’s struggles, I clip them to my screensaver, post them on my social media, and even print them out to put on my refrigerator or desk,” Dr. Serani says.
“Binaural beats are not very noticeable because the modulation depth (the difference between loud and quiet) is 3 db, a two-to-one ratio. (Isochronic tones and mono beats easily have 50 db difference between loud and quiet, which is a 100,00-to-1 ratio). This means that binaural beats are unlikely to produce an significant entrainment because they don’t activate the thalamus.”
  That said, you achieve the best results when you listen to the tones in a relaxed, quiet environment, investing your complete attention to the tones and the effect they have on your inner self. Experts recommend that even isochronic tones be heard via headphones to cut out distractions from external noises. The best thing to do is give it your entire, undivided attention, so that you can experience the outcomes quickly and easily.
Binaural beats require two separate tones from two sources that are combined inside the listener’s brain to form the target tone. The lower frequency sound is called the carrier tone, and it is combined with a higher frequency sound known as the offset tone. Because of this, binaural beats must be listened to with stereo headphones or the effect is lost. Binaural beats create a hypnotic effect, but they are not the most effective tool for brainwave entrainment, and binaural beats are often ineffective for people with hearing loss.
No. The frequencies are consistent throughout the duration of each music production we offer. It could be argued that a better approach is to change the frequency over time, starting at a higher frequency when the listener is alert and slowly ramping down as the music progresses and the listener becomes more relaxed. So why have we not taken this approach?
In fact just having a particular range of brainwaves running through our grey matter is also not “meditation”. Brainwaves are not the cause of the meditative state. They are only an indicator that we might be in a meditative state. And then again we might be in some other state as well. Those exact same brainwave frequencies are present during many different activities and states of consciousness, not just during meditation.

^ Trost W. and Vuilleumier P., Rhythmic entrainment as a mechanism for emotion induction by music: a neurophysiological perspective. In The Emotional Power of Music: Multidisciplinary Perspectives on Musical Arousal, Expression, and Social Control, Cochrane T., Fantini B., and Scherer K. R., (Eds.), Oxford, UK: Oxford University Press; 2013, pp213–225.