The only safe cure for serious fatigue is sleep. This sounds obvious, but many drivers try to fight through tiredness using strategies that simply do not work as well as they feel like they should.
Opening a window for cold air may feel refreshing for a few minutes, but it does not fix the real problem. Turning up loud music, drinking coffee, or stopping for a snack can help slightly and briefly, but none of these things restore the reaction time, judgment, and awareness that only sleep provides.
If you are too tired to drive safely, stop driving. Pull into a rest area, parking lot, or other safe location. A short nap of even 20 to 30 minutes can make a meaningful difference. If you are on a long trip, switching drivers is an even better option when it is possible.