The main cause of flu is a virus so tiny as to be invisible to the naked eye. However, such a tiny organism is enough to cause a man of 60-70 kg to lose his strength, and make him so exhausted as to prevent him walking or talking. Most of the time, the pills we take or the meals we eat do not do any good. The only thing we can do is rest and wait. In the body, a war takes place in which we cannot intervene.
 We are tied hand and foot by a tiny organism. In such a situation, what we should first remember is the following verse of Allah, in which prophet Ibrahim says:

He Who created me and guides me;
He Who gives me food and gives me drink;
And when I am ill, it is He Who heals me;
He Who will cause my death, then give me life;
He Who I sincerely hope will forgive my mistakes on the Day of Reckoning.
My Lord, give me right judgement and unite me with the righteous. (Surat Ash-Shu'ara': 79-83)