Below is a video simulation of a first-person experience of autism, starring Carly Fleischmann. She has an oral motor condition that prevents her from speaking, but is able to think verbally (and communicate through a keyboard, which is not used in this video). Her condition is not typical of all autistics, everyone is different. Having said that, the sensory overload depicted in the video is a common feature of autism.

There are a couple more first-person simulations here and here, both well-worth watching.