Hi mate hope you are ok.
I went through similar and mine flairs up every year or so . I normally take a course of tablets that sorts me out. But riding and exercise in general is an antidepressant and it always makes me feel better and takes my mind off it.
I don’t worry bout my heart rate now as I know it can go up to 180bpm when pushing hard and that is normal.
Its a hard illness that I don’t think I will ever be rid off as had it for a good few years now but as long as I go to the quacks early enough I am fine.
I have friends who say you just have to snap out of it I can only assume they have never experienced it ! The best way I can describe it is getting ducked under the water and not being able to get back up only there is no water.
Mine also used to be worst when driving in the dark for some reason 😀.
Just get out on the bike mate and don’t worry bout ya heart rate as it will get high and I would revisit the quack as there are tablets that help.
Iam assuming you don’t mind taking them.
Good luck mate