What Causes Feeling Of Shutting Off For Few Seconds While Lying Down?

i have been having this feeling of something shutting off and back on for a spit second. when it happens. my ears close and things are silent for that split second. i feel this when i am at absolute rest when i lay down at night and in the morning when i wake up before i get out of bed. i have been on heart monitor and the test was good . what could this be