I've fought after hurting my back so badly the night before, I couldn't bend down to pick up my luggage. Not saying it was smart, just saying.
Well if the flus over I dont see a big problem. If you still have the flu a fight is one of the last things you wanna be involved in. Go to a store pretty much any store in doesnt have to be a GNC it can be like Walmart or Big Lots you can fight all sorts of immune system supplements.