I had my bike laid horizontal for probably an hour or two on sunday... I removed the clutch cover, rearranged the clutch discs, then put it all back together. the gasket tore in two places (near the top... nowhere where oil sits all the time) so as a temp fix I used a bit of gasker sealer junk at those two places. I let the bike sit for an hour or so, then started it and put it in first gear (while on centerstand) to get the clutch discs nice and saturated.
this afternoon I went to ride to work, and noticed there is no oil pressure! (this is before I leave... the bike was running maybe 15 seconds total.. at most..) I immediately turned it off, and was like wtf. I thought maybe ALL the oil was on the left side of the motor... trapped behind the gasket or something.. so I leaned it WAY over on the right side... and checked the oil level (it looked good) then started it. waited 5 seconds or so and STILL no oil pressure.
at that point I took off my gear and got ready to take the car.. I decided ONE last time to start it.. and guess what? I have oil pressure. The light went off right after starting; as normal.
so what's the deal? first no oil pressure, now it's fine!
(cliff notes:
bike was horizontal on its left side during a clutch rearrangement. afterwards I had no oil pressure, so I laid it on it's right side and STILL had no oil pressure. let it sit for a min, and then it was fine)
All the oil probably leaked out of the oil pump and the pump lost its prime (the ability to draw fluid), and so it took a while for the pump to get working again.