Exactly, we are not to - and should not be - make a diagnosis. That is for a professional.

With that said, your friend sounds concerning.

Are you and others able to hold an intervention? Are you able to have an honest discussion with them?

The conversation could go like this?

"I am concerned about you. I've been seeing things happen that are worrying and I care you may find things getting difficult. Have you been noticing things aren't quite as they perhaps should be? This is what I'd like you to do.... I'd like you to talk to someone. Maybe you have an Employee Assistance Plan at work to contact? I hear they are very helpful. Perhaps you might call up your family doctor - I would be willing to go with you if you'd like."

Such words are not demanding and may not be confrontational. If however, your friend does get confrontational you need to be prepared to withdraw from the relationship until they make an effort to seek help or change their behaviour.