Try not to panic. Some questions:
How much hair came out?
How long had you been keeping your braids in before taking them out?
How long did you leave the PT treatment in for?
Has this happened before, and if so, what seemed to cause it then?
If you left your braids in for quite a while, you likely accumulated a lot of shed hair that got trapped inside your braids. The result would be that by the time you unwound the braids and wet your hair, all that accumulated shed hair would come out at one time, giving the illusion a bunch of your hair fell out all at once. ... But if we're talking about you losing handfuls of hair, that's another issue.
Protein treatments can cause breakage, but usually it's not that dramatic unless they've been done too often over weeks or months, and especially if they haven't been counter-balanced by moisturizing non-PT treatments (And you say you've been doing DCs too). The other situation where protein can really cause a problem is if you've left the protein in your hair for too long. If, for example, you're leaving PTs on your head for half the day or overnight.