10. "They told me at the blood bank this might happen."

 9. "This is just a 15-minute power nap like they raved about in that time-management course you sent me to."

 8. "Whew! Guess I left the top off the White-Out.  You probably got here just in time."

 7. "I wasn't sleeping. I was meditating on the mission statement and envisioning a new paradigm."

 6. "I was testing my keyboard for drool resistance."

 5. "I was doing a highly specific yoga exercise to relieve work-related stress. Are you discriminating against people who practice yoga?"

 4. "Why did you interrupt me? I had almost figured out a solution to our company's biggest problem."

 3. "The coffee machine is broken...."

 2. "Someone must've put decaf in the wrong pot...."

And the #1 best thing to say if you get caught sleeping at your desk:

 1.   "... And, finally, let us pray for the future of our company. Amen."