Sleep in the Back to the Future Trilogy

A few months ago, I got to thinking about sleep in the Back to the Future movies, specifically the recurring scenes where Marty McFly wakes up and is told "you've been asleep for [however many] hours."  I recently re-watched them all, and I think those scenes are meant to indicate a sort of time-travel jet-lag.  In the same way that people's sleep schedules get messed up after a lot of travelling to and/or through different time zones, Marty McFly's sleep schedule is messed up because of the time travelling.

Shortly after he travels to 1955, he's hit by a car and wakes up after nine hours.

"You've been asleep for almost nine hours now."

In the alternate 1985, he's hit on the head and wakes up after two hours.

"You've been asleep for almost two hours."

In 1885, he falls down an incline, hitting his head on a fence, and wakes up after six hours.

"You've been asleep for nearly six hours now."

Granted, he's hit on the head before each lengthy period of sleep, but in Back to the Future, Part III, he wakes up (without having been hit) and says, "Oh, man, did I sleep."

Before I watched the movies, I wondered if the number of hours he was sleeping before those recurring scenes had any connection to how far away (temporally) he was from the original 1985.  That doesn't seem to be the case, but I still think that there's something to the sleeping-as-time-travel-jet-lag idea.  Those scenes indicate that the time travel is - in some way at least - affecting his sleep.