It's not a burst supply line or the ceiling would have been down in about 15 minutes. Call a plumber please.

I would suspect either the drain or the riser from the shower controls to the shower head as being the culprit.

I would strongly advise getting a licensed plumber out to your house, and let that person determine the source and what needs to be done to fix the problem. If you have wet drywall ceiling, that moisture is most likely continuing to spread from the part that you immediately noticed into the surrounding portions of ceiling drywall, and if the spot began in a corner area that meets a side wall the moisture might spread down that wall too. The stuff commonly used in places outside of so-called "wet rooms" (bathroom, kitchen) isn't water resistant and it tends to suck up water like a dry sponge would.

It might appear that the leaking has stopped, but depending on the source, it could be continuing to slowly drip without you really knowing that is occurring. This is why you need a plumber to find and repair, but you should be prepared to hear that you'll also need to call someone to put in new drywall - unless you're okay with a big section cut out of the ceiling so the plumbing-related repair(s) can be done. :P