I ghosted my friend on his birthday. What the fuck? (A confession)

I ghosted my friend on his birthday.

I have known him for about a year. He had been planning for a small get-together with 4 close friends of his (me included). The day of his celebration came and he shot me a couple of texts, but I didn't respond. I didn't want to, nor did I feel like going. This overwhelming sense of anxiety(?) or was it discomfort(?) suddenly came over me and I ended up ghosting him on his big day. We haven't spoken since.

I don't know why I did what I did. I feel so sick and disgusted with myself. He had been a pretty good friend to me and he celebrated my birthday with his small group of friends and even gave me a really thoughtful gift. To this day, I don't know why I did that and I really regret it. I'm a horrible person that did such a ridiculous thing and I'm still trying to understand why.