Illness and MS . . .

For the last couple of times that someone in my family has come down with a cold or a flu or something like that, I have noticed that I get extremely tired. I don't usually get sick but I do end up spending the day/weekend in bed, fast asleep. This past weekend, I slept nearly the entire day on Sunday (I got up for a shower, went to church, came home, ate something and went back to sleep). I slept Saturday night, Sunday all day and all night. The next day, our youngest came down with diarrhea and felt awful. In the days that have followed, other kids have had it for an evening/day. Is this a common symptom of MS? Other people get sick and the one with MS just gets tired? It's happened enough that I believe that there is a definite correlation.
My wife and I were speculating about the mechanism. For instance it may be that your body is so busy repairing the damage from the disease that it leaves off repairing the MS damage? Your immune system kicks up a notch or two upon discovering the intruder and doubles it's attack strength both on it and on you? Just curious if something like this has been noticed by others.