Cross

So I was riding my 03 z400, did a wheelie and then it died about 10 seconds after the wheelie.. now when I try to start it it sounds as if tge starter is just free spinning.. and sounds like weak or no compression. But as I try to start it and let go the clutch it does try to move forward. Before that wheelie it was doing fine! I checked gas, spark and air filter. I'm confused. Unless I dropped a valve. Any help is appreciated thanks