Is it permissible to pray at home if one fears illness or another ailment, and what should he say to his friends regarding their fatwa?

We ask Allah Almighty to increase your eagerness for good. The reward for congregational prayer in the mosque is great. If you go out after performing ghusl from janabah and have only fallen ill once, this indicates that your going out to the mosque generally does not harm you. Therefore, you are not excused from missing the mosque prayer. However, if we assume that you are certain that illness will occur due to your going out, then you are excused from missing the mosque prayer, because the fear of illness is one of the permissible excuses for missing Friday prayer and congregational prayers.