DS (4) currently sleeps in my bed, I'm trying to get him back in his own bed but that's a whole other thread! For the past 3/4 nights I've been woken up by his whole body shaking quite violently. It's almost similar to how someone shakes when they are really cold (he's definitely not cold) but slightly more aggressive. It lasts for about 10/20 seconds although feels much longer, sometimes he sleeps right through it but others he wakes up really crying. The last two nights he's also had random spasms of his legs, last night his leg just kicked out 10 times in a row but it wasn't like how he would kick if he was awake, it was almost robotic as it was so quick if that makes sense.
Not sure if this is something that I should be worrying about or if it's just a normal thing for kids to do in their sleep?