J.M.
When my daughter was about 6 months old, I had her laying down on her back on the sofa, and I was leaning in and tickling her belly with kisses and shaking my hair in her face to make her laugh. One second she was laughing hysterically, the next time I "came up for air" (probably about 30 seconds later) she was sound asleep! I guess my "jokes" weren't as funny as I thought they were!