It's called orthostatic hypotension, it's not necessarily indicative of an underlying condition, and it's just a thing that happens every now and again to cyclists, because we participate in an activity that pretty much just uses the legs. Blood gets down there, wants to stay down there.
I have a pretty much perfect physical, am 2 years younger than the OP, ride a ton more (for a fair bit longer) and I'll still get a little bit 'o the woozies from standing up too quick (hopping up from the sofa) or rising from a bent down position, probably a couple of times a week.
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