I was stretching my leg and my muscles started twitching crazily..is this worrisome?

Depends: What medications are you taking and what have you been doing before you have the twitching - how long did it last ? Was it relieved by changing positions . Are you dehydrated ?It could be electrolyte imbalance .Or if its associated with back pain - it could be related to disc problem.

No: Twitching is common & happens to everyone; and is not dangerous -- usually just bothersome ... Sometimes downright painful! frequent twitching (in the absence of new meds, herbs, etc.) could indicate a deficiency of several salts: potassium, magnesium, calcium, manganese, selenium. A daily multivitamin can replace these salts if you are deficient. See your pcp to exclude more serious problems.