I remember before PFS I was that kind of person who was very weak and fragile..I was almost Always weak and with flu, temperature etc...
Since suffering from PFS I got the opposite, very tired (chronic fatigue) but never ever a flu/temperature and if I had, it was very rare.
Now I am having flue etc again, so I don't know if it is a good sign or not...
Good sign will be when you will feel connected and yourself again...it is difficult to say if it is good or not to get a flu.