Missed work, I feel awful. help!?

I have been a personal trainer with this company for about 4 months. I was out last night at a frat party and someone slipped something in my drink. I woke up after my cl. To say I felt like **** would be an understatement. My boss called me saying that there were 20 people and no one to teach. I don't know what to do!! I need an amazing explanation.