I'd worry less about my own mental health about being locked in a room and more about my husband. I don't know if he'd be in a good mental state when I came back after being home alone for a month, and I certainly wouldn't be in a good mental state after being locked in a room for a month. It could be marriage-ending if we ended up with enough problems, and is that worth 5 million? Not really. I'd probably look back and think "Life was easier, and I was happier before I got 5 million dollars... why wasn't I grateful for what I have?"
And man, if my cat died while I was in that room I would fall to pieces. Wouldn't be worth 5 million. He's just a cat but he's MY cat. He's in great health, but getting to be an old man.
Thanks for the mental trip. I really think I could last the month but there would be other prices to pay that might make it a terrible decision. Makes me grateful for what I have now!