I think the whole concept of a "runner's high" is fiction. I've certainly never experienced it and I've done exercise quite a few times over the last half century. I'd be pleased to get to the end of some exercise without feeling like I want to be dead (figuratively), or, if I've really pushed myself hard, like I'm about to throw up (literally). I usually don't arrive back with an improved mood, either - if I exercise enough it actually makes me aggressively grumpy and antisocial.

(Ah, just checked Wikipedia, and aha, it's a rare thing that most people don't get. Well, that explains that. Now if people tell me "oh, you just haven't pushed yourself hard enough, you'll get it if you just try harder" I can point them there. Some people just don't get it, same way some people won't just "meet the right person" and magically get married and live happily ever after like some of my relatives kept telling me when I was in my twenties.)

On the other hand, I've started back on the Couch To Five Kay thing (third time I've done it) and am half way through week two, so I think I can say I'm doing it regularly now. That can't be a bad thing, even if it makes me feel awful two or three times a week.