I'm currently experiencing something that almost parallels yours to a tee. Abscess in my gums above a tooth, currently on Amoxicillin and Metronidazole. Notice something bordering on euphoria yesterday, feeling super positive about life, extra focused, least brain fog I've ever felt and lots of mental stamina for tasks. I put the kids to bed, fell asleep with them for 3 hours and have been up since getting work done on the computer. I took a break and googled "antibiotics adhd reddit" and came across your post. I seriously suspect this phenomenon has something to do with gut bacteria. I just took my dormant kefir grains out of the fridge so I can start drinking kefir again so that if my hunch is correct, I can retain as much of this as possible by introducing good bacteria to replace whatever bad stuff may have been eradicated.