7pm hits and I can't keep my eyes open. It's terrible. Any suggestions for dealing with it?

If I'm doing something active in the evening then generally I'll be fine. But the second I sit down to watch a movie or read a book I find myself continually nodding off and then snapping out of it. My wife says I'm hilarious to watch but fun it is not.

If I go to sleep much before 10 then I'm awake too early the next day, so that's not a solution. Having a snack or cold drink has no effect. Caffeine keeps me awake all night so it's not an option.

My theory (guess) is that I'm getting dump of melatonin in the early evening and that what's making me so drowsy. I've played around with exposure to 'red' light at different times of the day but not noticed a difference in the evenings, but I really have no idea what I'm doing. And besides I don't know if the circadian rhythm is even the cause.

If anyone has any suggestions for short circuiting this onset of the flop sleeps every evening I would be very appreciative to hear it.