I am quite familiar with this. Just happened actually, and lasted approximately 30 minutes, and it caused me to google it. I have never gotten a concrete answer/diagnosis, but from all the people I have consulted(mother who is an RN, Neurologist), the best answer they can give me it that is has something to do with the eyes and how your eyes perceive physical movement.

It used to happen frequently as a kid(I'm 27 now). I'd say once a month or more. About an hour or so after a nice long videogame session it would start to kick in. I find it hard to believe that it is only eyesight, because there are certain subtle physical feelings I get when it hits full blast. I tend to get mild tingling sensations, and feel a bit of a rush of bloodflow to the brain.

Since puberty it happens once or twice a year. I think some of the posts on here are not experiencing quite the same thing as the original poster. It starts very subtle, where you can "sense" or "feel" a change in your mind(perhaps the rush of blood to the brain), but the physical "speed" of things is unchanged for a minute or two.. then soon you start to notice that sounds around you are louder (like a fan on low that you normally don't hear unless you focus your hearing on it, the fan suddenly sounds a little louder and faster), objects seem to act faster(like the blinking of an alarm clock that was unplugged and flashes 12:00), and your own body movements seem to be sped up ten-fold. You can wave your hand across your face and it "seems" like it went at 50mph, you can walk around and you feel like your walking faster than you've ever walked before. It's important to note that when these things are happening I am cognisant that I am not in actuality walking faster or waving my hands faster, it is merely a TIME PERCEPTION DISTORTION. I can get a little freaked out by it, but that's only because I cannot comprehend how it starts or where it comes from. I do not think this is panic/anxiety related at all.

I don't get a racing heartbeat, it can feel that way to some because of the aforementioned tingling/odd sensations you get in the head/body. It does seem more related to your own physical movements than exterior stimuli. The more I move, the faster things seem to get. It has lasted as little as a few minutes, as long as 45 or so. It does seem to fade slightly then poof things go back to normal. The process of it "starting" comes on more gradually than how it goes away.

I find it very perplexing that I can instantly "feel" the change in my brain when it starts, yet it is very acute and does not hit full-blown "speed up" for another minute or two. I don't remember much as a child, but I can distinctly remember this feeling and I know exactly what it is when it starts.

I've always found this to be very strange, but the one common theme was that after 4-8 hours of videogames was typically when it would happen as a child. It does seem to be random in adulthood.

The comments about inner ear could be on the right track, as it may have something to do with the equalibrium. But an eye/time perception distortion has been the best explanation I can give, considering the main symptom is your own physical movements "feel" fast but you also are aware that they are not in reality.

Thyroid is an interesting comment, I wouldn't mind getting that checked.

Hope this helps.