Choose Your Own Chemical Adventure

As you walk up the steps you hear the sound of footsteps coming from above. You look up to see a smartly dressed and considerably overweight gentleman hurrying down the steps towards you.

He doesn't appear to have noticed you. Suddenly realising that he's going to run into you, you cry out "Watch out, Mister!" and try to step to aside.

Too late! He collides full-force into you, knocking you flying. The man collapses on the stairs, the stack of books he is carrying being strewn all over the foyer.

What do you do?