Take a nap

Everyone has had this happen at some point in their adult working life. Maybe you didn't get enough sleep the previous night, maybe you had a huge pasta lunch o rmaybe you're hungover or (currently drunk!)
Your chair behind the desk is comfy, its quiet in the office, so you put your head down for awhile to rest your eyes. Just in case somebody walks in, like the boss, they have radar for these things. Here are a few things you can say:

"They told me at the Blood Bank this might happen."

"This is the 15 minute power nap they raved about in the
time management course you sent me to."

"Whew! Guess I left the top off the Whiteout. You probably got here just in time."

"Did you ever notice sound coming out of these keyboards when you put your ear down real close?"

Raise your head slowly and say, "...in Jesus' name, Amen."