Here is a Sample Apology Letter for Illness. You should modify this apology letter according to your need and situation.
Adam M. Anderson.R,
I came to know that you were affected by fever and cough which persists for more than a week since you have reached your residence after a period of stay of nearly 5 days in my residence.
I noted it down on the 4th day of stay in my residence and asked you regarding if you were sick. But you kept it closed within yourself and didn’t let me know regarding your sickness. If I had known about this on that day itself confirmedly, then I would have taken you to the nearby famous hospital and treated you immediately.
I understand that you were quite deterministic in leaving my residence due to your hurriedness expressed by you and your family to return to your native place. But it is equally necessary that you should take much care of your health than anything else.
I really apologize for making you to stay at the upper roof of the building along with me due to lack of space inside the room as my residence is quite small. I believe it is the only reason which had led you to your misery in health. I heard that you were not in a position neither to get hospitalized nor to get treatment in your home as your family members have went to your family function.
Your helpless situation makes me feel as a bad fellow. So being a friend I request you to grant me permission to stay with you till you recover.
I am leaving this letter, a day before I leave my residence meaning which, I will reach there as soon as this letter reaches you.
With Warm Regards,
Adam M. Anderson.R