I am not a doctor, just a parent of a type-1 teenager, but I do know that
muscle spasms are typical of low-blood-sugar seizures. It sounds like he is having seizures, just not severe enough to lose consciousness.
You say he has been low consistently, but don't mention if he also swings high. If he is running more consistently low, he needs to talk to his endocrinologist as soon as possible to see about reducing his amounts of insulin, or tinkering with his schedule of shots.