Do animals know that they're being put to sleep? Do they feel it, and Does Karma come around after it happens?

I had to euthanize my cat today after 7 1/2 years. She had a heart worm that the vets didn't see and could not treat. My husband and I had to feed/water her thru a syringe. Some days she would keep it down, but majority she would thro it up. She wasn't going to make it much longer it was just deciding when would be a good time to put her down. I felt we were being selfish letting her live so we could pet and hold her. This morning both of her hind legs were paralyzed and cold. She lapped a little bit of water and then thru it up. I picked her up and she cried in pain. When I put her on the bed she cried on every exhale. My husband and I took her to the vet and they let us stay in the room with her while they gave her the injection. I've never euthanized an animal before. I cupped her face in my hands while they injected her and she just stared at me. Literally 5 seconds later the Dr. said she has ped on and she was sorry. I looked at kitty and her eyes never closed. Did she know?