Years ago, when I was running, training for a half marathon, I experienced endorphin highs and just recently, I got to wondering if cyclists, notably, daily commuters, have experienced the same.
Given that running is much higher impact on the body and therefore, may be more likely to create endorphins, it is possible that it is less prevalent in cyclists.
I must admit that I don't know what the symptoms are except that a few months after the half-marathon (I continued running), I had a severe ankle sprain and was told to stop running for a few weeks to allow it to heal and when I was caught running a week later, I was told again to stop and that it was the endorphins that were "encouraging" me to continue. I did as I was told and the ankle healed. That's all I know about endorphins.