The most important one is probably the feeling that, "Uh-oh, now I'm not doing anything active to fight the cancer, and what if there are cells left in my body lurking somewhere that now will be free to flourish and grow."
It's also frightening because while going through treatment, women become accustomed to frequently seeing their doctors or nurses or other caregivers. Particularly during radiation, which is a daily occurrence, the techs that administer the radiation can feel like your closest buddies for a month or six weeks. To all of a sudden be cut off from people who have been so reassuring by being told by your doctor, "Okay, you're done, see you in six months," feels as though you've kind of been pushed out the door precipitously.
The last thing is that because chemotherapy particularly can be so physically arduous, many women have used all of their emotional and physical energy just to get through it day-by-day. When the crisis is over, and you have a chance to sit down, you think, "Oh, my God, what did I just get through?"
How does it affect families and friends?
Most people's family and friends are hugely relieved that it's over and are more than ready to have life get back to normal, though it might be embarrassing for them to admit it. By the time the months of treatment are over, they've really had it, even if they've been wonderfully loving and supportive and helpful all along.