how long was it on its side? just hook the battery up to a trickle charger. And give it a shot. depending on how long the bike was on it's side, the fluids probably ran to one side. Same thing happend when i was teaching my gf how to ride my ZX6R. She dropped it and since it was on the ground i showed her how to pick it up, it was on its side for about 5mins and had trouble starting afterwards. Had to wait about 10mins before it would fire up.
2008 ZX6R - K&N Air Filter, PCIII + Ignition Module, Frame Sliders, Black Puig Windscreen, Intergrated Tail Lights, Kleen Mod, Fender Elim. 6000k HID's, Yoshimura Full Titanium Exhaust, -1/+2 and Speedo healer