Wow, thank you guys so, so much for all your amazing responses. I really appreciate you taking the time to explain what might be happening here and it makes a lot of sense. Looks like it's overtraining then. Thanks so much for the advice!
The Test will be in less than two weeks. I'll follow your advice and take it easier. Can't do longer low-intensity rides on weekdays so I'll keep doing that on the weekend, paired with commuting in a humane pace and 1 mock test training session. If you've got any more suggestions, I'm all ears.
work4bike as for the low blood pressure, it's always been 100:80 to 90:60 for me (when rested, not during training). My heart is otherwise healthy. It runs in the family. I feel normal, not like fainting all the time
My partner says my low blood pressure may be in part responsible with the high heart rate, though it wouldn't explain why it's been increasing.
As for my rested heart rate, it's around 64-70.
Thanks again to all of you for your help and support. I really appreciate it!