It depends a lot on department culture. Some departments are really fragmented, the professors hate each other, etc. So if you're in a department like that then not only will you be stressed out from all the work you are doing but you will also be miserable. That's why it's really important to get a feel for the place by visiting it first but even then it will be hard to get a read on the culture. Doing research 5 days a week really wears you down if the people around you doing similar work are assholes.