I also had a bean sprout that was like a week old die overnight two days ago. It was perfectly healthy and totally dead the next day. That plant was in the ground and in a sunny part of my yard. It is monsoon season here so its 100+ and humid.

Well, firstly I'd say it isn't dead. It's just looking a bit tatty. In a black pot! In July! In Arizona! I'm actually amazed it's alive at all. Your spearmint's ancestors live in damp places in cool climates. It isn't at all surprising yours isn't happy. I'd put it in a larger, non black, pot in fresh soil in full shade. I also would experiment with not watering every day unless the plant indicated it needed it. It looks much as if it is rotting.