I was misdiagnosed with non-Hodkins lymphoma and I was incredibly scared. Went for a second opinion and the doc read my test results and the report from the other hem onc and chuckled saying "This guy shouldn't be practicing medicine. You don't have cancer." Most relief I have ever experienced. That being said I have known some people with cancer and watched them go through their experiences.
At the moment, my mother-in-law, who is truly a very nice person that I enjoy quite a bit has recently begun her journey with Stage 4 Endometrial Cancer. She went through her first round of chemo three weeks ago and feels like shit. Her outlook on life is fairly matter of fact, she is getting her affairs in order. She got a therapist almost immediately after the discovery that it wasn't just isloated in her uterus and had spread outside. She says that it is helping, but that it is hard to stay positive knowing the statistics.
The majority of people I know who have survived cancer (4 out of 6) came out of it stonger and more positive than before. One of them does Iron Man competitions now or something equally insane. The other two lost a lot because of the cost of treatment and are very resentful about that. That resentment causes them to be negative people who are very hard to spend time with. I know that the 4 positive ones saw a therapist throughout treatment and went to support groups and did everything they could to survive. They treat every day above ground as a blessing.
I hope that your treatment goes well. Be brave and stay positive and you'll very likely get through this. Find support and start therapy ASAP.