I travel a fair bit for my job and I have noticed similar patterns. Did some research related to it and found that it is attributed to changes in cabin pressure, oxygen levels, low humidity, and how long you remain seated in those cramped conditions. I try to load up on water prior to the flight, take some NSAIDs (like ibuprofen, etc.), and I try to get up and walk around a bit during the flight to restore circulation. I have found that help lessen the impact on my system. I still feel a bit run-down, but I am able to bounce back a lot faster. I hope that helps!

All the best,
SFN Warrior