Sensory overload is a common occurrence for those of us on the spectrum. In fact, it's a key trait of ASDs.

I get them several times a week normally. If I'm forced into more social situations or into busy environments such as cities or shopping centres that number can increase to several times a day pretty easily.

My mum has told me it's pretty obvious if we're out somewhere and I start to overload because I look like I'm there but I'm not actually there. She'll catch me just staring at something or standing with my eyes closed as I try to block out some of the stimuli, or if she speaks to me I just mumble a response but it's not actually anything to do with what she's asked me because I'm making a concious effort to hear less haha. If I'm at home when it happens I retreat to my room, close the curtains (I have blackout curtains) and sit on my bed with my knees pulled up to my chest and rock. As a child I used to close myself into the bottom of my wardrobe when I got overloaded, this was actually one of the reasons my parent's first sent me to a psychiatrist, though that guy was useless and just gave me anti depressants...

If I don't catch sensory overload in it's early stage, it has a good chance of pushing me into a complete meltdown, which is neither pleasant for me to experience or for those around me at the time to witness.