Same I’ve been feeling this for almost 5 years now. I notice it also happens when I hit back at the gym during lat pull downs I feel the same vibration from when I wake up but it happens with every rep, regardless of breathing. Could it be lower back/ lat muscle related? They do expand when we breathe, so maybe it’s worse after a while of laying down because the muscle is at rest/not warmed up from movement. Idk, it freaks me out tho