ok so this is kind of a weird one but bear with me
I've been bouncing around southeast asia for the past couple years: mostly Thailand, Vietnam, Indonesia, that whole circuit. And the one thing that kept destroying me wasn't food poisoning or scams or any of the stuff people warn you about. It was jet lag.
Not even the big intercontinental ones. Like yeah obviously London to Bangkok is gonna mess you up. But I kept getting caught off guard by the medium ones too. Flying from Bali to Japan, or Singapore to India. 4-5 hours of timezone difference doesn't sound like much until you're lying awake at 3am in a hostel staring at the ceiling for the third night in a row.
And I noticed something that none of the "jet lag tips" articles ever really explained well — direction matters way more than distance. Going east absolutely destroys me compared to going west the same number of timezones. Turns out there's actual science behind it. Your body's internal clock runs slightly longer than 24 hours naturally, so it's easier to stay up late (westward) than to force yourself to sleep earlier (eastward). Flying east from Bangkok to Tokyo felt way worse than flying west from Tokyo to Bangkok even though it's the exact same distance.
The other thing I figured out the hard way: when you land matters almost as much as how far you flew. I used to just book whatever flight was cheapest without thinking about arrival time. Huge mistake. Landing at 6am in a new timezone and having a full day ahead of you is completely different from landing at 11pm and trying to immediately sleep when your body thinks it's mid-afternoon.
So I started doing math before every trip. How many timezones am I crossing, which direction, when I Iand, and based on that, when should I seek sunlight, when should I avoid it, when should I eat, when should I force myself to stay awake. The rule of thumb I settled on: ~1 day recovery per 1.5 timezones going east, ~1 day per 2 timezones going west. It's not perfect but it's been surprisingly accurate for me.
After doing this on paper for like the 20th time I thought screw it, I'll just build a tool for it. I run a small flight route site (https://departuremap.com) so I already had airport timezone data sitting around. I wired it up into a simple calculator, you pick your origin and destination airports, choose when you're arriving, and it spits out the timezone difference, estimated recovery time, and actual useful tips like when to get sunlight and when to avoid it.
It's at https://departuremap.com/tools/jet-lag-calculator if anyone wants to try it. It's free, no signup, no email gate or anything. Just built it because I needed it myself.
Couple things that have actually helped me beyond what any calculator can tell you:
Melatonin is a cheat code for eastward travel. Low dose (like 0.5-1mg, not the 5-10mg pills they sell in the US) taken at destination bedtime for the first 3-4 nights. Works way better at low doses weirdly enough.
Morning sunlight is everything when going east. I used to hide in cafes with my laptop. Now I force myself to sit outside for at least 30 minutes in the morning even if I feel like death.
Don't nap for more than 20 minutes on arrival day no matter how tempting. I've ruined so many first days by "just resting my eyes" for what turned into a 4 hour coma.
Eat on local time immediately. Even if you're not hungry at their lunchtime, eat something. Your gut has its own clock and it takes cues from meal timing.
Honestly the biggest thing I've learned is just respecting that jet lag is real and planning for it instead of pretending it won't happen. I used to land and try to power through and then wonder why I felt terrible for a week. Now I just accept that the first day or two is going to be rough and plan accordingly.
Anyway, just wanted to share this since I see jet lag questions come up here all the time. Happy to answer anything about the calculator or jet lag stuff in general: I've basically turned this into an unhealthy obsession at this point lol
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