What do you suppose it was that tapped my shoulder?

13 yrs ago i gave birth to a baby boy. i breast fed him. his dad slept in another room my son with me. i had a short string of xmas lights on the wall that i used for night light so i can see him when he woke for a feeding. well one night he woke up eyes big as saucers i was so tired as i'm feeding lying on my right side i begin to doze off. so there i am nodding off still feeding him. all of a sudden i feel these 3 taps on my left shoulder i gasp and look behind me. nothing there . i thought it was his dad but no one was there . i got scared oh i got very scared so scared i decided to stay awake until my son was asleep. this really happened . don't know what it was . pls help. thanks.