How to create a sleep effect with progress bar

Hello to you, I need your help. I'm making a mod with dinosaurs and I would like to be able tame them. For that you would have to feed them while they are asleep, and they are put to sleep by shooting tranquilizer arrows at them. Wich raises a bar of torpor puts them to sleep from the moment it is full. But which goes down gradually and wakes them up when it is empty.