We left our cats for about a week while we had our baby moon and wedding anniversary holiday. Our cats were left at home with a woman we hired to come in every day, feed them and play with them. They love her and they're much, much happier at home than boarding somewhere. We stayed with DH's parents for a few days then on our first night in the nice hotel, we got a call saying one of them had had some sort of seizure, so the woman took him to hospital. DH was half resolved to fly back the next day, as he couldn't that night, but did get a friend to stay at our place for a few nights so the other cat wasn't alone. It was an anxious worried night.
Next morning he was eating, washing himself and using his tray so they sent him home, having no idea what caused the seizure. When he got home he was quiet and sleepy but otherwise normal. And when we arrived home he was very much his usual self, barring a few "attacks" (no fits, thank goodness) where we have managed to care for him and help him out.
But it was that night our realised that our cats were more than pets, they're part of our family.