Oh my, Shay, I am sorry to hear what you have been going through. That is horrible.
It sounds like whatever you had been feeling during the day might have set off the flashback. Most feelings like depression are thought based (though some can be body chemistry, though in your case I don't believe that to be true) and although you may not be aware of your thoughts, that is what brings you down. It can trigger things like flashbacks if you are thinking anything related to what you went through.
You mentioned feeling sorry for yourself. Was it about what you have been through in the past or the work you are doing now?
I wonder if part of what you were experiencing is the result of the reaction you had from D when you told her about what happened to you. She was compassionate and caring. You mentioned many times that you felt very supported and maybe a little taken back by her reaction (pleasantly surprised, maybe?). Sometimes when a person shares something so deep and gets such a wonderfully warm response, it can trigger feelings around how traumatizing the event really was. People do not typically react with such support unless the situation was bad, so in the back of your mind it may have triggered your depression over it. Also, you have been going through a lot lately with the flashbacks, telling D, the situation over Linda (though it turned out, it was still very stressful) and your recovery in general. Your strength may be down and therefore your ability to cope as well as usual.
You also experienced a very good insight recently with your feelings of self blame around the attack. I'm not sure that you were aware of how huge that was for you. Before you really accepted what you had been through, you were thoroughly convinced this was your fault. Your defenses were very high and you had many arguments against any thought that you could not be at fault. That takes an enormous amount of energy to defend. Just the fact that you let go of those beliefs can open a new door to other feelings. And it can change your perspective so you now see the reality of the situation more than you did before, triggering strong feelings of depression.
I know you feel embarrassed about what happened to you last night, but P and Linda want nothing more than to help. You went through something absolutely horrifying and your needs are understandable. This is your time to recover, Shay. All of us have times like these in our lives, where we need others to support us and help us through. God is not going to put all these wonderfully compassionate people in your life and not allow them to be used in important ways. He made this to be your time, with the right people, right circumstances to help you through. He knows what you need and will provide you with it. And I think what you experienced is normal. You had a flashback and got upset, so what? How awful that Linda and P had to talk to figure out a solution to help you. I bet they both felt so put out! You have needs Shay, there is no shame in that. You would be there for either of them wouldn't you?