Yes and no. Sewer gas is a lot of methane. Some people don't react well to it.

Also, the smell is bad enough to make a lot of people sick to their stomach.

If you have it in your house or apartment, you should take care of the cause of it. Is that the case with you?

Methane, but it's hydrogen sulfide that smells. Sewer gas in a home isn't going to kill you, and if you feel sick and fix the plumbing and feel better, you won't have long term effects (that anyone knows of). But workers in large buildings, ships, and underground tunnels lose their lives every year, not from methane ordinarily, which rises, but from the sulfide, which sinks.
You can smell it in concentrations of .5 parts per BILLION.
Gov't regulations call for gas masks when it might be 20 parts per MILLION.
It take 500 PPM to possibly kill a person.