Yes, but not to explain why or apologize to everyone. Although I will ask Sis to make up something to tell her kids and not tell them the truth about what Auntie did.
It will be a note explaining to my Sis that I have chosen to CTB and explaining the preparations I made so that things would be easier for her. E.g. combo for my safe to access important papers, contact info & documents for prepaid cremation services in case my body is found, info for the landlord to get security deposit back to her, info on the bank accounts I will have added her and my brother to so that they don't have to deal with probate or wait for proof of death, pre-filled out tax papers ready to file, how to have title to my car transferred, etc.
I will have already boxed and labeled things I'm leaving to her and my brother and disposed of charitable items.
Finding a good home for my dog will be the hardest prep item, but at least there is time.
Anything else I'm forgetting that a note recipient might find helpful?