Why is it all say i can live a normal life with 1 kidney, in the same breath say you cant do this and that ?

am a truck driver, just found out i have reno cell carcinoma. after 3 oppinions they say i have to loose a kidney, and there is a strong chance that it may have spred out side if some membrein, which means kemo or radiation or both. but what gets me is the dont's. they say i can do any thing that is no jarring, no bouncing nor extreme strenuous activities. doesnt sound like a normal life. all i know in work is physically extreme what scares the mc jevers out of me, is that this a very agressive cancer and could be the gateway to death. finding it was a fluke, was really sick, vomiting and fever, diarea. past out, dr's say i had a mild heart attack from the stress of vomiting but the stomache was so expanded they thought something rupsured, so a CT scan and they found this out. now i cant sleep b.p.'s up eating is haywire hell every thing is haywire. mar.19th i go in for the opperation. looking for solis in a world of confusion help