That's what happened with the Spousal Unit the other day. Long story short: blood clots on the lungs. The doctor spoke to us post-treatment and said, "I normally have this talk with the widow."
Yep, he dodged the Big Bullet, only because he's been so active up to now. But lately he's been sitting a lot because he's doing a lot of writing (working on a screenplay).
So I bought him a Fitbit and told him to keep moving. I understand sitting for long periods; heck, I do it all the time. But I also get up and move on a regular basis.
The moral of the story: move it or lose it -- lose it all!