Hi there - Just checking in because it sounds like my DS is living at your house! :-) He is exactly the same age and has gone through exactly the same thing - the worst of it was from about 20 months to just recently. Some days it's worse than others but it seems to be tapering off. I too had no idea what was causing it, and it seemed when I tried to intervene (comfort or whatever - even just sit near his crib to 'be there' for him) it made things worse. Major, screaming fits and no-no-no for like 20 minutes. We thought it might be teething as well, but meds made no difference. As I couldn't determine the cause, I have just chalked it up to the terrible twos - who knows what's going on in their little brains that are developing so quickly at this stage? The fact that he also sometimes even chants no-no-no while he is sleeping leads me to believe that this is just something that can't really be 'fixed' and (as we're starting to see now) will pass with time. It is unpleasant for sure, but I settled for doing what I could - i.e. sitting with him to show him that even if he can't handle whatever big things he's feeling, I can. Not sure that this helps, but wanted to let you know you weren't the only one! Good luck!!