While cabin pressurization may be a factor in "that jet lag feeling" the biggest factor,by far,is the body's "internal clock".I've done a fair amount of east/west traveling in my day (and also a fair amount of shift work in a hospital)...some of the flights having passed through 10 or 11 time zones.When that little clock says "time for bedtime" yet detects bright sunlight every part of your body gets confused...particularly the brain.The result...jet lag.
It also has to do with hydration.
Here’s an article about it....