Pretty great, but in my experience with a time where I was struggling/my boss was struggling/a coworker was struggling (different times), nobody is ever going to answer this question truthfully and everybody will think you're a threat for asking it.

list of things that in my experience may help if you suspect someone's not right:

* not eating alone

* eating at all, but the above makes it likelier

* when people give feedback that can be difficult, and instead of expecting the person to have an answer or excuse ready, build in time "off" with no f2f

* during difficult meetings or occasions where outbursts are narrowly averted, ask the person their opinion after. feeling listened to helps.

* if the problem is someone is working "too hard", 100% they kind of hate their non-work lives. They may actually also hate work but work is something predictable. Send them to a conference somewhere.

* people who have no friends will usually tell you so in exactly those words in the right circumstances. Believe them, it's a huge (huge!) contributor.