I need and want the aftercare. The more things we try and the further I push my boundaries, the more I will find myself overwhelmed. There have been times after a session where I will lay there, feeling fine, and the next minute my eyes well up and it takes a few minutes to regain my composure. I definitely agree that some part of our brains can interpret what's happening as abuse (especially if something hurts more than we were expecting it to), which makes aftercare very important.
I think it also depends on the relationship. Some subs may not need any aftercare, others may only need physical reassurance, and others might need to be talked to and verbally reassured.