Sleep

The jet lag guide is a light-and-melatonin protocol timed to how fast the circadian clock can actually shift, not a folk remedy list. The insomnia reset works through timing and light exposure in order, because most sleep advice skips the order and wonders why nothing sticks. The melatonin guide takes the take-it-every-night question seriously, including what the heart-failure research did and did not show. The cortisol guide covers the part most people get backwards: disrupted sleep and a disrupted cortisol pattern travel together, and it's rarely obvious which came first.

Alongside them sit the measurement questions: what catching up at the weekend does to the rest of the week, and what an HRV reading is worth once you know the reference ranges by age. They link back to each other where the science overlaps.