Struggling with this child!

I have a child I won't name. If you know us well you most likely will know who it is anyway.

So, this child is scared of some any things. Literally - we cannot watch Scooby Doo, Duck Tales, and Atlantis type movies scare him too. These are just a few!! Sometimes the music on games gives him nightmares - I guess the suspenseful sounding stuff(?). He sleeps on the floor because he is scared to sleep on the bed - still can't figure out WHY!!!

We have seen here and there where he needs to know things ahead of time to be able to handle "things".

An example, he loves to have sleepovers at my parents. He will beg to have one. However, if you spring it on his last minute he is a crying mess. Literally, hiding under their table crying, with the thought that we can;t say good bye and of course, can't leave. He has to have 2-3 days notice - even with something he LOVES!!!

Today just clinched it. At the Y you have to be a certain age to go to the BIG kid zone. HE has had a rough time with the fact that his brother can and he can't. There are so many things that he can't do that we chose not to make an issue of this one. Older brother is waiting for him to be big enough. He has been waiting for 3 months and wants to "go to the Y on his birthday so he can go to the big kids' class". Well, they are slightly busy today and the main guy said the older one could go so I explained why we were holding off and he said "Oh, his birthday's in a week, he can go too." Any "normal" kid would be excited, right?? As we head upstairs he begged me to let him stay downstairs. By the time we got up there he had tears!!! I ended up making him stay up there because I just didn't have the time to keep going back and forth but it was horrible on him. He did have an ok time but I only stayed 1/2 hour because I wasn't sure how he would do. He didn't look thrilled when I got back but hard to get out of him whether it was good or not.
I try to give him notice as much as possible but sometimes it just isn't an option and I need to teach him how to cope with that. I can't deal with these meltdowns every time something unplanned happens. Do any of you have tricks to help?