How To Write A Letter When Someone Is Ill . They may want to reply, but they may have mislaid your card, or be too tired to get to the post office. Explain why you are writing. FREE 8+ Formal Sick Leave Letter Templates in PDF MS Word Google from www.sampletemplates.com Thank you for telling me about your illness. When we learned of the serious nature of your illness, we were both shocked and saddened. I hoped it would go away by this morning, but it looks like i’m still above normal temperatures.