5month old thrashing his arm

[lovelymama]

My 5month old DS has started thrashing his left arm up and down all the time. He can be sitting in his chair playing, or lying in bed and he will just start thrashing his left arm really hard. I'm not even sure if he's aware he's doing it but it's freaking me out. Is it just a development phase or is he frustrated/sign of tiredness (he started doing it last week when for some reason his sleeping turned from pretty good to absolutely horrendous!)

My DS did this from about 4-6 months and we thought it was really weird as well! No idea why, but he's now 6.5 months and hasn't really done it for a few weeks. It did coincide with his worst period of sleep as well but I think bad sleep is par for the course with a 5 month old. He used to do it a lot in his bouncy chair because it seemed to get the chair bouncing - not sure if that was the reason why he then started doing it everywhere else!

Thanks HQ. Thought it was normal but as usual I like to over-analyse every part of my son's behaviour. Need to chill out!

Ah, sounds like our DSs could be twins and we could be twins too! I am trying to chill out, but that usually only lasts for about an hour before he does something else unexpected and weird

I decided one arm thrashing was a developement stage because all three of mine did it and later though slightly less noticeably, added the other arm. DD2 would hold a doll or chain of plastic links in her hand and thrash it up and down for ages.