I have worked with you for the past [number] of [years/months] and Your sudden drop in productivity really concerns me. I would like to make sure that you’re still happy and satisfied with us here.
I talked to human resource, and they informed me that you haven’t used any of your [number] vacations for the year. Maybe it’s time to take a some time off and unwind.
Please don’t think you’re in trouble in any way. I am just genuinely concerned. You haven’t been as active as you usually were these days. It hasn’t been the same without the old you.
If something’s wrong, please let me know. My office is always open for you.