Just like when he backed out of that fight with zuck

Depression isn’t the same thing as sadness, and I wouldn’t be surprised if it disqualifies someone from being an astronaut. Most people don’t have depression, but everyone feels sadness at some point in their lives.

To answer your question, astronauts are trained to work under extreme stress, so they would know how to compartmentalize the pain and focus on completing the mission. Similar to soldiers.