Overworking myself for a good reason?

So this past March I was blessed with an incredible opprtunity. Great compensation, great team, great mentorship, great WLB, great name to have on the resume.

The compensation is more than I've ever had. The position is fully remote. The company hasn't done any "mass" layoffs. The team (except one guy) has great WLB. In fact my manager has told me not to be like that guy, since he's not your average joe. The company specifically says they don't reward long hours.

Yet I find this all makes me anxious. I've worked 15 hour days just because I want to feel useful. No one asks me to do this, but everything seems to point to this being a complete fluke and it can all go away in a snap.

It's fully remote, in a saturated field, great benefits and pay, and many people have called it their dream company. In other words, I feel incredibly replaceable and it makes me work twice as hard.

I feel like I might be on my way to burnout if I don't correct myself. Has anyone been in this position before and how did you deal with it?