'Weaken immune' system is usuallly given as a side effect of anorexia, and I know a lot of people report having lots of minor infections which I assume is due to this. I've always said I was lucky to have a strong immune system as I hardly ever catch colds, flus etc. However it's hard for me to say whether I'm ill as I feel pretty rundown/sick most of the time, so I only notice symptons like runny nose, sore throats etc. What's got me wondering is that on the couple of occasions when I have caught a infection that's going round, I tend to get the same symptoms as every one else, but over a much shorter time span- whereas they might me sick for a week, and spend a couple of days with aches, then a sore, then a cough, I will get through the whole thing in a couple of days, with each symptom lasting a couple of hours, and be back to 'normal' a lot quicker. To me this says overactive immune system, but also suggests I spend too much time monitoring and worrying about my health, and try to 'diagnose' things that I don't even know exist.
I guess this raise a more general point about how hard I find to judge what 'good health' is, and when something is severe enough to warrant a doctor's attention. If I told them about every niggling worry they'd be seeing me every day, and I don't want them to mark me down as a hypochondriac/attention seeker, in case they stop listening, or don't take me seriously when I ask for help.