Thanks for all the replies! I guess the general consensus is to keep this to myself and look for ways to get in earlier.

I suppose I was hoping someone would be understanding about it at work, but the points you have all brought up are true. I doubt I will be replaced (thank goodness), but my annual review might not look too great if people think I am not doing enough work.

I hope that there will come a day when people struggling with any MI can be upfront about it with their boss and work together to look for solutions.