It's a 3kg bag of vitamin C, which I have used almost all so I don't think it's something in there. It could be related to the cold as Gaby mentioned.
Judging by the response here, it seems that it's not a common occurrence anyway so I'll keep the same mega-dose protocol the next time I fall sick.
Judging by the response here, it seems that it's not a common occurrence anyway so I'll keep the same mega-dose protocol the next time I fall sick.