now that I think of it, I do get a sensation once in awhile of something going across the top of my foot. nothing there, just my nerves. so look into that too.

It may be "restless legs". You can get a feeling of something crawling on your legs and you feel the urge to move them and cannot keep them still. I get it now and them and it is miserable. It usually happens when you sit down to relax or when you get into bed at nite. Just a suggestion.

It could possibly be the way you are sitting, you could be pinching a nerve. Try moving around in your chair and see if that helps.

Do you have a plant in the room? We have a plant in our computer room and sometimes I start feeling gnats or mites around me. Sometimes I see them sometimes I just get feelings as you are describing. I put a drop(just a drop or two-too much will kill the plant) of liquid dish detergent in the water and water the plant. This kills off the gnats. I learned this from my mother.
So, if you have a plant, give this a try.

Are you Diabetic?
It could be Neuropathy.
J J

perhaps mites? I am allergic to paper mites (hence I keep my book collection wrapped in plastic) and sometimes they also munch on cloth (minuscule amounts so we don't notice).

'NO SEE UMS''they do exist.While visiting my Mom in Fla yrs ago the same thing was happening to me and she laid a paper towel on the table and handed me a magnifying glass there were hundreds off them but move the glass and I could not see them.

I agree with most here. Consider what position your legs are in when you feel this. Are you cutting off circulation somehow? Does it stop if you change position?

Are you on a water pill for blood pressure? Had to change my meds...very creepy feeling in my legs at night.

Could be circulation. At night at times I feel something strange near or above an ankle and actually see a tiny vein forming below the skin, but near the surface. Weird but not worrisome. Sometimes there is not sign of anything happening. Probably just nerves jangling!