Radon gas - really?

I was told my home indicated an unhealthy level of radon gas. I only know this because I had an inspection to sell the home.
So, I received quotes from companies to "mitigate" the radon gas to an acceptable level. Now, this process was full of interesting people and I needed to choose one. Really? How do I choose?
I decided to choose the company that talked the most about what they were going to do - instead of what the other companies would not do.
The discussions reminded me of politicians. I never like to vote for people who tell me what someone else does wrong - just tell me what you are going to do right.
So, I hired the company that didn't talk about the other companies - and they did a good job with the "mitigation process". Now, after the second test, my home has low levels of radon gas present. That is a sigh of relief!
However, how long have I been sleeping while inhaling unacceptable levels? When did my home go from "passing" to "failing" in the radon department? Somewhere between 2003 and 2011.
Now, the testing company said we should get our homes tested every 2 years - really?
As a homeowner, I have never thought of radon gas - never.
And, finally, do I inhale unacceptable levels of radon every time I am outside?
I don't want to minimize the truth that radon gas can cause lung cancer - but, if it comes up from the ground - and is bad to have in our homes while we sleep, how do we live without breathing it in when we are outside?
If you have more education on this than I do - please share :)
Radon gas - really?