Yeah, it's a nocturnal myoclonic jerk, as Tillie said. It's not related to ALS.
I started having leg jerks while asleep when I was 28. I didn't know it at the time.
After a couple of years, it changed. I began to feel the "need" to jerk just before the movement. You can't stop it. You have to bounce.
After a decade, it became bodywide. Occurred just before sleep, whenever I would relax in a chair, or when sitting in a car or airplane for a couple hours.
Another decade passed, and now it can hit me almost anytime of the day or night. My arm, leg, or whole body can jerk so hard it'll knock me out of my chair.
Your neurologist might prescribe clonazepam/Klonopin or pramipexole/Mirapex or gabapentin, perhaps. There are newer solutions, too.