People might get hypnic jerks when doing this
.... My son 
has been doing the "jerk", as I call it, from the moment he was... [DOC] [TLE] Here's Why Your Body Jerks Awake When You're Falling Asleep ... [PAR] Feb 22, 2016 ... Or it might mean your quality of sleep is being affected by things like stress, ... 
Alcohol is another huge factor  many people get hypnic jerks... [DOC] [TLE] Hypnic Jerks - Sleep.Org [PAR] Find out more about hypnic jerks -- that feeling of falling that you get while trying 
... Up to 70 percent of people experience them occasionallybut no one knows... [DOC] [TLE] Hypnic jerk - Wikipedia [PAR] A hypnic jerk, hypnagogic jerk, sleep start, sleep twitch or night start, or jump, is 
an involuntary twitch which occurs just as a person is beginning to fall asleep, 
often causing them to awaken suddenly for a moment.