I have become increasingly worried about DS2 and his "shivers". He is now 15.5mo and keeps having these episodes. He is not cold, he is not feverish, he is not upset. His bottom lip will start going first and work it's way to his whole body. He will continue with his usual activities and completely coherent apparently without noticing anything is wrong. It makes him fall over and unable to eat properly. Each episode will last from a few seconds to a few hours, some with strong effects, some weaker.

I have been unable to obtain any information over google thus far and don't want to appear foolish to a doctor if it is just something minor. Another thing is that whilst talking to my midwife friend about it (she had no ideas either), I was reminded that during my pregnancy, my stomach would often shake and that I had been worried back then. So this has been an ongoing thing throughout his entire life, womb and beyond. Has anybody had a similar experience at all?

Additional health information
I had many complications during my pregnancy from conception
He has digestive problems and is unable to tolerate dairy (it's the proteins in that), lentils (again with the proteins as they are similar to that which is in dairy), pumpkin, sweet potato, tomato, strawberries, chicken, fish and something else as I know I'm forgetting one atm. He has had digestive problems since before birth as well.
He appears to have a compromised immune system. He has had a simple turned out of control fungal infection for the past 3-4 months.
Developmentally average-advanced and 97th percentile for height, weight on 95th.