I recently met my old classmates that brings painful memories for me

Hello again, I feel the need to write something personal here.
Today has been enough of a bad day; lack of sleep, late to post a dissertation topic, having my dissertation topic denied due to its irrelevancy with my major--all seems fine but my mood soured when I met my old classmates from high school who I initially thought forgot about me. By forgot, I mean to ignore me, because I would rather not interact with them.

Having a bad day is stressful enough, but having my past memories of my unpleasant days of high school was enough to make me feel oppressed. I don't know, memories soon rushing inside my head and I was stupefied. One of them noticed me and greeted me, saying if I remember them. I know I'm taught to forgive but I instinctively lied and said that I forgot who they are and fled the place I was at. Then I became riled up, I ranted to my friend about how much I wanted them to ignore me and to forget. Because I never wanted to see them ever in my life, as if prickled by needles the moment my existence is acknowledged by them. I don't know whether they changed but I felt sick to my stomach and lost my appetite soon after seeing them.

I fear that the once outcast me in high school would be dragged away back to that hellish place where I felt I'm against the world. I wasn't very well liked due to how "abnormal" I am in school, and being reminded of what I should have moved on from suddenly and uninvitedly appear like that petrifies me. I've never been to a therapist or a psychologist, I know I have problems but I seriously need some advice on what to do. My mind's a jumbled mess and the hate and rage still lingered in me even as I grow up.

Any feedback would be appreciated. Thank you and good wishes for everyone here.