This is not a conventional prayer. It is a gratitude prayer based on putting trust in Lord and giving thanks in advance.
Let's get ready to cure your flue Inshahallah.......
This prayer requires that you put one hundred percent faith in Allah's ability to cure your fever and give extreme thanks for the favour you are going to get in the form of cure.
Step1: Sit in a quite place
Step2: Imagine that you are in the future and Allah has cured your fever with His mercy, power and infinite intelligence. See yourself one hundred percent healthy as this will indicate that you have full faith in the Creator's ability to heal you.
Step3: Let Allah/Lord know how much grateful you are for this huge favour by feeling intense gratitude. Imagine yourself repeatedly saying thanks with genuine feelings of gratefulness.
Do this prayer session after every Salah. Try to do it as often as you can as it will fasten your results.
I guarantee that if you can complete the three steps with passion and energy, your flue will disappear like it never occurred. Gratitude is the strongest symbol of surrender to Allah - the Creator of Heavens and Earth.
Practise this prayer and let me know how well you did.