Questioning my own existence / extreme dpdr

Hello everyone.
I've recently started taking a SSRI for my depression. I no longer feel extemely depressed, but at the same time, I feel like I don't exist. My own existence freaks me out. It's like I'm doing things in autopilot, there's no more "me". I'm also scared because I've realized that there is no objective component to my existence. It could be a hallucination, a dream, stuff like that.
Everything I experience is from my point of view.
But now, I can't even prove that. My very own existence. Everything feels distant, I feel like I've lost that last spark that kept me going. Does anyone else question their own existence/feel like they aren't truly existing? How do you deal with not being able to prove that you exist objectively?