You finally get to that deep, restful, theta state and suddenly your body involuntarily jerks, pulling you back to the fully awake state. These movements are called hypnic jerks. These are very common for 60-70% of people as they drift into that state between awake and sleep.
Hypnic jerks often accompany hypnagogic hallucinations and are the body’s reaction to sensations, sights and noises from inside your head. Why these happen, science isn’t sure, but there are a few hypotheses.
The first is that it is simply the act of nerves misfiring during the transition into sleep. The second is the thought that the twitching is an ancient reflex that happens during the relaxation of a muscle during the onset of sleep. It is believed that this is a protective mechanism to keep muscles from becoming too relaxed and allowing primates to fall out of trees.
No matter what the reason, it can be annoying to finally reach that deep restful state only to be pulled back to waking reality.
While getting rid of the reflex may not be possible, there is some evidence that points to stress, anxiety, fatigue, caffeine and sleep deprivation can actually increase the frequency and severity of these hypnic jerks. Floating can help with a few of these and with regular floating, you may see a decrease in these disruptive spasms.