Cat psychologist please

[indignatio]

1 year old neutered male has just returned after 96 hours out. He is thin and dopey, so we think he was trapped somewhere.
Vet has said to keep him in. I initially rejected this thought as he has (imho) been deprived of his liberty for the last few days so keeping him in seems cruel. However, as he doesn't seem alert, I worry he might not be aware of danger. Whilst he was around the garden, I didn't worry, but only 7 hours after returning, he was out of sight and we worried big time.
Really don't know what to do for the best
Any advice would be appreciated

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I would follow the vet advice. Being dopey would worry me that he is injured/poisoned and may need urgent attention at some future point. Keeping him in would help him to be assessed/recover.

I’d keep him in too.

Do as the vet advises. There's a big difference being stuck in an unfamiliar shed with nothing and in the dark versus home with many rooms, water, food and known humans.

If he continues being dopey then the vet will want to know what he's eaten, how much, drank any water, peed or pooped or slept. You can't give that information if he's disappeared. Next time you see him lock him in your house and observe. You don't need a psychologist, just common sense.

Is keeping him in any more cruel than putting him outside when he's dopey? I honestly can't believe your thought process here.

Keep him in for a couple of days so you can get him to a vet if he needs help.

If he’s been eg stuck in a shed, in the heat, he’s probably dehydrated. Give him wet foods that he likes. Tuna in water, cat milk?

You are only guessing what's happened to him, and they don't think the same way we do anyway.

Keep him in and under observation, and make sure he is eating and drinking properly. Check his litter tray for normal wees and poos. If he deteriorates in any way, get him to the vet urgently.