What does it mean when a guy puts his head on your shoulder?

we were sittin on the sidewalk, and my friend said he needed a 'head rest' haha and then he slowly leaned over and put his head on my shoulder for like 2 seconds and then sat up again...he has done some other flirty or idunno kinda things in the past. do you think he was more tired or does he like me? If you were to put your head on somones shoulder what would you of been thinking?