making the sound of a motorboat. This could also mean that you are so tired that the desire to sleep is just as large of a drive as your sex drive. You would rather do both motorboat and sleep, so you choose to motorboat some pillows.
To fall asleep so hard that you bury your face between two pillows. This often leads to some snoring and
Man I can’t keep my eyes open! I am staring at the bed trying not to motorboat pillows.