Hey, it’s John.
If you’re lying there at 11 wondering why your brain won’t shut off, the answer is usually something that happened eight hours earlier.
Caffeine’s half-life is roughly five to six hours. A 3 p.m. cup is still working on you at 9 — about half of it is still in your system. And here’s the part people miss: it doesn’t have to keep you awake to cost you. Caffeine late in the day measurably reduces deep sleep even in people who swear they drop off just fine.
The cutoff I’d use: eight hours before bed. Bed at 10:30, last coffee at 2:30. If you’re sensitive to it, make it ten.
The other 3 p.m. problem is the long nap. Under 25 minutes and before mid-afternoon, naps are fine — good, even. Past 30 minutes, or after about 3 p.m., and you’re spending the sleep pressure you need for tonight.
What to do instead when the wall hits: ten minutes outside, or a flight of stairs. Both work faster than coffee, and neither one borrows against tonight.
Decaf after two. That’s the whole email.
— John