Having just endured yet another 12-hour aircraft flight, I am more than ever a skeptic about the actual reasons for "jet lag". Jet lag in the typical account is said to be a function of a disruption to the individual's normal pattern of sleep and wakefulness.
I think it's simply a matter of being forced to sit in a tiny little chair for 12 hours without a break.
When I get home I will take a few days to recover, and then I will sit in a tiny little chair for 12 hours in my lounge room, whilst inhaling the concentrated exhalations and exhudations of 500 grotty people. I'll let you all know how I get on.