Sick and stressed out about performance

I have recently received an increase which has increased my charge out rate to clients significantly. This has caused me to become overly conscious and stressed of my time.

I have also fallen ill recently and because of deadlines and feeling a sense of duty to complete work, I chose to work instead of take sick leave, I have not gotten better.

I feel now that this was not a good idea as I feel my performance has been hindered due to feeling ill and the medication that I am on.

Should I write an email acknowledging that my performance was not up to par or should I just leave it and wait to see if my performance gets mentioned.

I do not want later when it is mentioned to be seen as making excuses as I do definitely know that my performance was not up to standard