Is it dangerous to sit in front of a gas heater?

I used to sit in front of a gas heater like this and literally lay and sit half a meter from it in Winter.

So for 3 months a year almost every day, I would sit in front and watch TV for many hours – for years. Now I’m starting to wonder if it’s had an impact on my health, specifically my brain.

I’m paranoid that breathing in the fumes has caused damage. (It uses natural gas.) Any helpful information is appreciated.