You were not really specific about how long this has been occurring, if anxiety, stress is involved etc... You are not alone in this type of occurence. Please look up Somatoform Disorders, primarily undifferentiated somatoform disorder, and conversion disorder. This may possibly assist you.
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it's probably not worth posting here after so long, even if i did have something helpful to say, but i'll do it anyways... YES! i have the same exact thing happen to me, except it lasts a little longer, and sometimes feels like my legs are above my head. usually happens when i'm looking at a screen in the dark. it's been happening to me for an awful long time, and if i had to guess i'd say it's some form of mild seizure. just my best guess. seems harmless anyways. now i doubt you or anyone else will ever read this but since you know what it's like to sound nuts i'd like to share some other weird stuff that happens to me. i get flashing lights in the peripherals of my vision when i close my eyes, again, usually aftyer looking at a screen in the dark. deja vu, yeah that's pretty normal but it happens a LOT. something i can only refer to as "fast forward vision", which happens almost exclusively while driving or riding in a car. i know that one sounds especially stupid but it's almost like all of a sudden i can see at a super high frame rate. hard to explain. this next one doesn't happen much to me anymore, but was very common for me as a kid. things seeming infinitely far away or close, and infinitely small and large. not actual objects, but things i'd imagine, or sometimes just the general sensation. happened in dreams a lot. anyways i'm sure there's some reason that people experience weird stuff like this, but it seems harmless, and that's both the good and the bad news. good news because... well obviously... harmless. bad news because that makes it unimportant to figure out. so we'll probably never really know why it happens