tha welcome to the forum. You started off with a good question.

If you do a search on the word abuse in just the forum titles you will find several discussions on whether abuse leads to BDSM. These could be helpfull.

But your question is a little different. Now that BDSM has come into his life could his reaction, sleeping, have anything to do with it. Counslers will remind us that excessive sleep can be a sign of depression. And my experience tells me that BDSM is more than capable of bring to the surface memories of past abuse. And dealing with those memories, especially by yourself, can lead to depression. So could the two be related, posibably.

In either case the main issue that I see is your boyfriend being able to confront those memories and work through the issues and problems they bring about. Weather you deside to continue with you BDSM activities or not this is always going to be an issue for him. The good news in your post is that you know about. It will take time for him to work through this and I would suggest seeking out the help of a counslor. Your help will be important in this process as well. I would suggest that you also talk with the counsler some what as you will be an important part of the healing process. Suffering the abuse is bad enough, and the healing is difficult and can take some time.

I know some others will some more to add.

Good luck to both of you.