This isn't good. Woke up this morning and went down to the kitchen (where Ziggy sleeps every night) and instead of having a lively, cheerful, purring cat meet me, he was still asleep on the table top. Since then he's been very lethargic and just wanting to sleep. He doesn't seem in distress and he sounds like he's breathing alright, but just seems unusually tired. He ate most of the food I left our overnight, and he now snoozing on the bed, but this is very unusual behaviour.