I had an appointment 20 minutes ago. Literally why I didn't post yet today.

This is often called “waiting mode” and there are strategies to help deal with it. For me, that’s alarms. If I have an appointment, I’ll set alarms for when to be in the shower, out of the shower, and out the door. It allows you to actually relax.
- /me keeps checking alarm and that I have it set right, how much time until the alarm goes off vs the event the alarm is set for.
- That's a great idea and helps with one of the big things that triggers waiting mode for me. To add to the conversation of techniques, another factor of waiting mode that I experience is the avoidance of task switching ("I don't want to start doing this only to have to stop doing it suddenly"). For this, perhaps adding an alarm earlier as a heads-up to prepare to switch tasks might be helpful?

This is one of the worst parts of it for me. I can't enjoy a late shift at work because all morning I'm just dreading going in. Same with any later appointment, too. Even plans with friends at night is stressful.
- I would doom scroll in my bedroom for hours before going to my night shift.
- Just do what I do and sleep during the day. Get some good blackout curtains and an eye mask. One of those sunrise simulator alarm clocks would be a good idea too.

catch me spending 6 hours stressing over an appointment that’s over in less than 20 minutes

Still have trouble, but after being medicated, it's amazing what a difference it makes. Now I'm only disabled (by exhaustion) after the appointment; not spending the hours before the appointment frantically checking the clock and doing nothing else.

Is this an ADHD thing?
- Can be. I’m always on edge about forgetting and being late to appointments due to time management issues, so having an appointment late in the day means I’m fixating on it all day.
  
  Hmm, I see. I do this all the time as well. Always wonder with memes can I just relate because they're ordinary human reactions or traits or actual indicators of some kind.

I hate this part of the brain. I have an appointment at 2pm. Why must I be awake at 9 and... waiting. Anxiously.

I calculate how long it will take me to get ready and get there so I can procrastinate to the last second without having to rush.

Looking for a flat, you do visits in-person here. 6 flats in 2 days per week is ok, 3 flats in 3 days has proven too stressful.

The way I've (sorta) gotten around this is to meticulously plan the day before the appointment, even if it's bullshit like "play videogames from 11a-2p". Hell, I usually don't even stick to the plan, just use it to get me started on doing something until it's time for whatever.
- When I meticulously plan to play videogames I always end up doing housework or working on some other project instead. My adhd won't even let me have fun unless I'm not supposed to be.

Had someone ask me if I was interested in applying for a position that was potentially opening up on his team yesterday and I've been stun locked since that conversation. I haven't even applied or anything yet...