Yes sitting a lot (airline seats?) is an issue for those affected. I had a biz colleague who was prohibited from flights > 1 hour because of clots.
my mother and I are prone to clots. Always have to keep moving.
If someone “did” have a concussion - it is possible inactivity could contribute to a clot.
“If” someone had a concussion in the first place.
Your comment reminded me of David Asman of Fox (Business) News. Back in 2005, he and his wife had flown to London. She had gone down to the hotel's gym, to get in a little exercise before they went out for the evening. She ended up having a stroke, and I believe it was from her sitting on the plane for the flight overseas. He wrote an opinion article for the Wall Street Journal about their experience with the British healthcare system, but unfortunately, it's no longer available at the link provided in the FR thread from that time.