You cant level-up if you in the duration of losing the cock-fight.
Check SPA for your MOJO, maybe expired and need re-service yourself at spa.
Check Equipment, maybe you were swapped some clothing/cars/jewels without noticing.
I sudden jump to lv 24 (from 20) after my recovery from cock fight...
while there I swapped gears to increase MOJO before Cock recovers.