Just wondering what happens in a "wellness check"?

I had one called on me today just because I took a long nap and didn't answer my phone. The person told me I needed to leave my phone on in order to avoid this in the future. As someone who has terrible insomnia, is on a ton of text lists and currently gets a lot of unwanted calls, this simply isn't going to happen. I'd never sleep! (And I don't want to be a slave to my phone.)

I woke up in time and had the wellness check called off.

I…

Usa "wellness checks"…what happens?