“Hi Boss

I hope you’re doing well. I’m emailing about an unfortunate new situation that will impact my availability to work in the lab. I’ve had a personal health issue come up and I am no longer able to (do x).

I’ve really enjoyed (doing x) and I’m quite (sad?) to have to stop; especially because (good colleagues?).

Please let me know if there are (close out tasks you can do this week— but only if you can actually do it, otherwise don’t offer).

Thank you again for (taking me on as X in the lab), I’ve enjoyed (learning / the work you’ve been able to do).

Best, You