Training & Nutrition - Twitchy legs?

I've gotten into cycling recently. I'm not in great shape and I'm terrible at running. I've noticed that when I've been riding for a while and stand up, my right leg will involuntarily twitch causing my foot to quickly rotate up and down on the pedal. I thought this might because I'm just not used to exercising so much, but once when I had a close call with a car, both of my legs were doing this uncontrollably for nearly 10 minutes! I was only a little shaken up but I couldn't stop them from shaking. I stopped for a few minutes to try and walk it off and then I was fine. Has anyone ever experienced this?

This often happens to me if I sit in a certain position on the bike, and I've been cycling for about 12 years. Not uncontrollably though. Try gently warming up before every ride then stretching your leg muscles before and after every ride (never stretch 'cold' muscles).

This often happens to me, but i dont know if this is the same scenario but whenever i do any kind of workout (lifting weights, running, biking, etc.) without stretching i start twitching really badly.

I get it when I lift weights too. It's probably just a result of the muscles getting a work out. It doesn't happen as often now that I've been riding for a few weeks and my stamina and probably strength too have increased a bit.