My mom is a vet, and I've learned from her how horrible it is to make an animal suffer. We had a poodle that lived from when I was 4 until when I was 17. I absolutely adored that dog. we put her down in our house, and I held her while she died. I'll always remember that day. It was hard, but she is in a better place.

You made the right decision; don't beat yourself up. Manic, depressed, stable, whatever...saving your pet from suffering is a good thing to do.