iPhone 5 battery error

Today, when my battery was around 30% (can't remember what percentage exactly) it switched off just as I was taking a picture on Instagram. Literally, as I pressed the button to take the picture, it switched off like it does when the battery is drained so because I knew I didn't have particularly low battery, I tried turning it back on, and the no battery logo came up, so I left my phone for around an hour as I was out, tried turning it back on again randomly by pressing the menu and the lock button and holding it down (which I had also tried previously) and it came back on with 28% battery.

I'm glad it's back to normal, but the reason I'm posting is because I'm wondering if anybody else has had this experience, and if I should expect it to happen regularly, or if it was just an error which doesn't really need a genius appointmet for or anything.

Thank-you. 🙂