The Flu is fucking horrific! Had it once several years ago and was unable to move for days. Started to hallucinate,ran a fever, the whole lot.
When I was finally able to drag myself to the GP she asked if I had any episodes of bursting in to tears while ill (which I had). Apparently the Flu can cause severe depression on a temporary basis.
Took me about a month to fully recover and must have lost about a stone in weight.