Well that sounds like a very scary and painful experience! Here is the good news . . . nothing is showing up now. What exactly that was is a bit of a mystery but an aneurysm does not appear to be the cause. The pain you had all of a sudden and that intensity sure are symptoms of an aneurysm. But the diagnostic tests don't show it. Unlikely they'd miss that. https://www.mayoclinic.org/diseases-conditions/brain-aneurysm/diagnosis-treatment/drc-20361595
Have you asked your doctor about something called a thunder clap headache. https://www.mayoclinic.org/diseases-conditions/thunderclap-headaches/symptoms-causes/syc-20378361
But here are also exercise headaches. Did this occur after one of your bike rides?
Lastly, there is something called an Ice Pick headache. It also is very painful and I've suffered this type myself. https://www.medicalnewstoday.com/articles/317234
Are you saying this happened years ago and not since? I'm confused I guess why you're so worried now if the problem went away. The time to worry would be if it came back again, but apparently it hasn't. There are a lot of things in life that can make us hurt that aren't going to show up on a diagnostic test. When you twist your neck violently all kinds of things can happen, including what happened to you. Too much exercise on a hot day without sufficient electrolytes or water can cause a lot of pain. It also could have been a migraine, as you had them after that. My first one happened when I was 13 on a day I didn't eat in the morning, it was really hot, and I went to play basketball. I continued after that to get them periodically for several years. But MRIs don't show that kind of thing. If after 4 years it's never happened again, there's really no way to get a diagnosis. And if it was an aneurysm, I'm guessing there would have been other problems, such as cognitive problems and a difficult recovery period. I'm guessing whatever it was it wasn't that, and given you felt pain in your neck, it most likely came from there. But I don't think you're going to be able to find out unless it happens again and you see a specialist at that time. I'd forget about it and go on with my life, and know that MRIs can't see what isn't there and often not what is, either. Peace.