Sometimes, not often enough to make me worried, I'm really really sleepy and I fall asleep for maybe 5 minutes or maybe less. I then dream something like falling down while walking on a sidewalk and reflexively try to cushion the fall with my arms. Then I wake up with mild spasms, because these reflexes are actually at least mildly executed in real life. It happened while watching a friend play Playstation and it happened in a lecture. In both times the friends beside me found this rather amusing. Well me too. (It's not painful) I wonder how normal this is, or what the real trigger are. Does anyone have similar experiences?
This has definitely happened to me before. If I fall asleep during a lecture, I sometimes begin to dream and if I fall down during that dream, my arms (irl) will flinch out in front of me a bit and I will wake up. Fortunately, usually nobody notices.
This is quite common. The explanation I was given,  was that the spasms cause the dream and not the other way around. Like your muscles twitch involuntary and then your brain invents a dream to explain what's happening. It might seem like a minute but it all plays out in a split second.
I've heard these mini-dreams referred to as "dreamlets" also.
It happen with me too. My hypothesis is that your unconscious mind think you will die when you fall a sleep. It's like the Celtic way to think: You die every night when you sleep. And rebirth at the dawn. Too much spiritual for me.
The term for this is a hypnic jerk. I think most people experience it from time to time. Wiki article says there's a hypothesis that it is a vestigial reflex that prevented early hominids from falling out of trees while sleeping.