Honestly, I think that's what traumatic experiences do to us sometimes. I had to go visit a doctor at a hospital where I've had bad experiences before and I felt my heart rate go way up. We all have associations- there's nothing wrong with you. As for your issue, if you could change the day, I would say do that but it doesn't sound like that's an option. So, I would keep the appt. Remind yourself over and over that there is nothing special about Wednesdays, but also have compassion for yourself and for why you have that aversion in the first place. Things are looking great, I am sure you will be fine, but I'm sorry you're having this hiccup. As juliemam said above, hopefully you can take back Wednesdays!
Thinking of you!