Don't blame yourself Mariah, those thoughts come up from time to time. I know that it isn't good for me to focus on but I have also learned that even little things can cause serious problems.
I'm ashamed to say this but maybe getting it out will help with the healing.
Stoney was a Lab/Chesapeake Bay retriever mix. He was a VERY intelligent dog who liked to play dumb. When you were around he would do dumb things and act like he didn't know what you were telling him at times but when he thought you weren't looking he would show his true intelligence. I don't know how many times my ex and I yelled at the kids for leaving the gate open and letting him out. Come to find out he knew how to open the gate himself, caught him when he didn't know I was watching.
Anyway he became an outside dog and my ex and I just stopped keeping him current on heart worm medicine. After a long time he got an aggressive skin infection so when we took him to the vet they discovered that he also had a severe case of heart worms. The vet said that they could try and treat him but it would probably kill him in his weakened state so we decided to put him down. That was one of the hardest things that I have ever had to do.
I will have to try the deep breathing if I wake up at night, couldn't hurt.
Have a great day.