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.

Brainwave entrainment is a colloquialism for such 'neural entrainment', which is a term used to denote the way in which the aggregate frequency of oscillations produced by the synchronous electrical activity in ensembles of cortical neurons can adjust to synchronize with the periodic vibration of an external stimuli, such as a sustained acoustic frequency perceived as pitch, a regularly repeating pattern of intermittent sounds, perceived as rhythm, or of a regularly rhythmically intermittent flashing light.
Another consideration of stress is whether it is acute or chronic. “Acute stress” is what an individual experiences at the time the stressor is encountered (4). The stress response is activated, and the body returns to homeostasis once the challenge of the stressor is removed or the person successfully manages the situation. For example, an individual on the way to an important meeting gets into a traffic jam and realizes she is going to be late; the stress response starts. When she calls her boss and learns that she can conference into the meeting while on the road, the stress response subsides with the resolution of the situation. When an individual experiences acute stress on a consistent basis, such as with overcommitting at work or constant worrying, it is referred to as “acute episodic stress” (4). Individuals who experience acute episodic stress often show signs and symptoms of stress (Table 1) that can negatively impact physical and psychological health. These individuals can learn how to change behaviors and manage their stress to prevent these consequences.
Practice positive self-talk. It's easy to lose objectivity when you're stressed. One negative thought can lead to another, and soon you've created a mental avalanche. Be positive. Instead of thinking, "I am horrible with money, and I will never be able to control my finances," try this: "I made a mistake with my money, but I'm resilient. I'll get through it."

It might seem obvious that you’€™d know when you’€™re stressed, but many of us spend so much time in a frazzled state that we’ve forgotten what it feels like when our nervous systems are in balance: €”when we’€™re calm yet still alert and focused. If this is you, you can recognize when you’re stressed by listening to your body. When you’re tired, your eyes feel heavy and you might rest your head on your hand. When you’re happy, you laugh easily. And when you’re stressed, your body lets you know that, too. Get in the habit of paying attention to your body’€™s clues.
You can practice visualization on your own or with a therapist (or an app or audio download of a therapist) guiding you through the imagery. You can also choose to do your visualization in silence or use listening aids, such as soothing music or a sound machine or a recording that matches your chosen setting: €”the sound of ocean waves if you’ve chosen a beach, for example.

It cannot be any wonder then that we are almost desperate to find some sign, some indication that meditation and brainwave entrainment is having tangible, definable effects. We seize on these odd little experiences like ‘flushing of the face’ or ‘seeing spirals of color’ when our eyes are closed, hoping these are signs suggesting the elusive relief we’ve been after is finally within our grasp. We ask others to validate our experiences so that we can reassure ourselves we’re on the right track at last.
Entrainment is a term originally derived from complex systems theory, and denotes the way that two or more independent, autonomous oscillators with differing rhythms or frequencies, when situated in a context and at a proximity where they can interact for long enough, influence each other mutually, to a degree dependent on coupling force, such that they adjust until both oscillate with the same frequency. Examples include the mechanical entrainment or cyclic synchronization of two electric clothes dryers placed in close proximity, and the biological entrainment evident in the synchronized illumination of fireflies.[13]