Dear Hanging-On,
Keep hanging-on! Take a look at the following website:
http://www.parentingyourcomplexchild.com
The woman who wrote the book and created the website has been through a lot.
I understand the "why" question. Sometimes it's karma, a stiff wind, a smell, a taste, a worry. Anyway you cut it, it's still driving you nuts.
I get the sense that you're trying to get a grip on something that you very well may not get a handle on. If they could answer "why" they could cure it. You're the voice of frustration responding to the childs cry in the dark. He's bouncing off the walls because something is stimulating him. Today it could be a tv show; tomorrow it could be the smell of cookies baking; the day after it could be something you read to him. It's often the way these kids express themselves (happy, angry, tired, sad).
Try a "weight vest" for the running into walls, etc. goes on. It's supposed to give them "sensory calming" when they can't seem to stop going for that need to feel that "impact". Is he getting occupational therapy? If so, ask them to look into brushing techniques, weight vests, etc. to help him stop looking for the impact.
Hates baths but likes the hose? Try installing one of those removable shower heads that let you take it down to rinse. He might soak the bathroom, but it could help.
Adding my hugs to you (I have to take Heckle, Jeckle and Clyde up to the 1.5 hour fight that we call bedtime!) and I'll check back with you.
Feel free to pm if you just want to talk with someone who's "so there" with you right now! (you don't EVEN want to know!!!).
Beth