Rek'sai spell casting

I was in the middle of a game trying to make a comeback and it was working. however, I got caught out by the adc Draven and support blitz I thought I would die but had enough lifesteal to kill Draven and run away from blitz. but for some reason after I burrowed while running away i couldn't cast my e, i later found out I couldn't cast anything. I was basically carrying my team and it cost us the win thankfully it was a normal but that is still pretty irritating and would love some help on knowing what exactly happened to me.