I also work in the oil industry and am dealing with anxiety/depression and possibly bipolar. I didn't want to talk to my boss about it, but he had noticed a behavioral change and asked if I was doing ok (out of honest concern). I talked to a friend who convinced me that I should be truthful with my boss. I was. He moved me to a more suitable project on my request and has allowed me FMLA leave. I work 6-hour days right now instead of 8. I have the option to take time off if I need it, even if that means I'm not at work for days/weeks. A good company will understand their employee needs. Companies cannot discriminate against one's health as a reason to terminate them. I think you should be honest. If your boss doesn't understand, then they are missing the bigger picture: Mental illness is an illness, just like cancer or anything else. It's serious - yes there are unfortunately stigmas - but you deserve to have the treatment you need and your workplace will hopefully understand.