Dear Sir/Madam,
Respectfully, I beg to inform that my name is _________ (name) studying in _________ (class/course) in your esteemed school/college.
Through this email, I formally request you to grant me ____ (days) leaves as I am not well. The doctor has advised me to take a complete bed rest for at least ___ (days). I promise you that I will try to cover my syllabus as soon as I recover. In this regard, I request you to kindly grant me leave from __/__/____ (start date to __/__/____ (end date)
Therefore, I once request you to approve my sick leave request. If you have any concern regarding this matter, you can contact my parents at __________ (contact details).
Yours faithfully,
___________ (Your Name),
___________ (Contact details)