Diane,
Do you think you body burden is down enough so that you are not redistributing mercury when you use ALA to pull mercury from your brain?
I would do a process of elimination to find what is the culprit. Maybe take a rest from the ALA for a while and keep everything the same and see if that helps. If not take a break from the dmsa and see.
I have never been on SSRI's thank God but I know of people who thought it was impossible to come off those blasted things and went through a horrible time. I'm betting this is what is causing you so much trouble.
When I took a trial of ALA I had terrible feeling of impending doom, like the whole world was going to end any second, after being off the ALA for a couple days, my brain started calming down.

Another thought is...... your mercury level is coming down and other "infections" and rearing their ugly head. Have you heard of the onion analogy? You peel one layer off and other layer is there to deal with.
hth