The abstract of a fascinating 1995 review paper by Maria Casagrande and colleagues which gathered experimental data together to try and work out which of the brain’s cortical hemispheres falls asleep first.
It turns out, it’s the left.
Which hemisphere falls asleep first?
Neuropsychologia, 33(7), 815-22.
Casagrande M, Violani C, De Gennaro L, Braibanti P, Bertini M.
Behavioral tasks (reaction times to acoustic stimuli and finger tapping tasks) performed by normal subjects when sleepy or attempting to fall asleep have been used as indices of hemispheric asymmetries during the sleep onset period. Results show a stronger impairment of the left hemisphere (right hand) both in reacting to external stimuli and in sustaining endogenous motor programs. The left hemisphere seems to fall asleep earlier than the right hemisphere.
Link to abstract of scientific paper.
Mind Hacks 
Just read the paper. The participants were selected for right-handedness. This has more to do with your handedness than anything.
F1000 biology recently featured a paper from Biological Psychology on the same topic (and with the same conclusion).
Here’s the pubmed cite:
http://tinyurl.com/2fojl4
F1000 biology recently featured a paper from Biological Psychology on the same topic (and with the same conclusion).
Here’s the pubmed cite:
http://tinyurl.com/2fojl4
Handedness serves as a proxy for the “handedness” of the brain. If you didn’t control for it, then any effects due to one hemisphere falling asleep before another might partially cancel each other out.