If you want to talk heart stuff, I'm always available. What's your relationship like with your cardiologist?
That sounds like a good plan. It means that you aren't getting enough blood to your brain when you exercise. That puts you at risk for all kinds of stuff. I'm not a doc so I am limited in what I'm comfortable putting out there, but suffice to say that it's a problem. Have you thought about alternative forms of cardio? I use an exercise bike at home because I don't trust strangers to help me if I keel over out in public.
It's understandable you would be hesitant to give it up. I have never experienced 'runner's high' so I can't comment on it personally but those who like it seem to like it a lot. I have my bike set up in front of the TV connected to my computer. Bike time = Destiny/Overwatch time.
I think I have seen maybe 10-20 total hours of sunlight since the fall, I hear you. Get your hardcore exercise in a safe way, then maybe take a walk or something outside as a cooldown. I am enamored of 'constitutional' walks around the pond at my apartment complex. After that, the last thing I want to do is to sit indoors.