Can someone explain to me what that jolting thing is that some guys do when they're sleeping?

My experience has been that both sexes do that (I know I do, I know my spouse does). Sometimes it is a reaction to nerves... like restless leg syndrome sort of. Or sometimes I will wake with a start if I hear a noise I do not associate with something familiar (an old leftover military trait..). Or I roll over to a position where a pin or wire presses on a nerve... sort of like an unwanted electrical shock...LOL

My spouse does it when her breathing becomes restricted (think...tongue blocks airway...happens much more often when she has sinus congestion. Or she is simply dreaming.... and sometimes talking in her sleep...some conversations are interesting...some not so much. But something that will ALWAYS wake her (and consequently me) is when she dreams a demonio is chasing her....

I get that sometimes..

When I get a really bad nightmare

It is usually an age thing. Your brain produces a chemical that keeps you still... you lose that more as you age and your muscles are more likely to jump as you try to sleep.

It’s actually your brain thinking that you’re about to die so it gives you a jolt. True story. Look it up

Rapid eye movement. Causes you to act out your dreams.

Could be something called a hypnic jerk. Give it a Google...

Hypnagogic jerk. Also happens just before you fall asleep.

Maybe they are pumping up their morning wood?

Only guys do that ?