I am working for a company right now who interviews counselors for different programs (not educational programs but general counseling services). We often ask them to talk a bit about something which happened in the past, what they learned, and how they coped with it.
If I were interviewing you, I would be specifically looking for what you learned, if you coped, and what kind of support networks you have if you were to have a problem now. For me, what exactly the issue itself isn't too much of importance. Nearly everyone I interview can think of one difficult time they have had (and if they can't they are lying). I don't want to judge you for what you did in the past BUT rather what you are doing now and whether or not you would be okay in my program. I want to know you are not going to just drop out on me if something bad happens, have developed effective coping strategies, and if you have to that you have some kind of support to hold you together.
Normally, if someone says they had a support network of family and friends to help them they usually pass my questions just fine.
If this was early on in your undergraduate career, they may not worry about it too much. Usually, the last few years are what the focus is.
--One last note. If they do ask about it. Pay specific attention to what they ask in the question. Often, I ask how someone "feels" about something and I get answers about what they would physically do, etc, but not the feeling words I am looking for. If they asked how you coped, answer the question, don't give a lot of background (unless needed). Don't give them any reason to feel like they need to know more about it.
Sometimes, when asked about their past, people jump to the part they know, have thought about, or understand, but don't always answer my question.
(These are just my suggestions from an interviewer's perspective. I haven't interviewed anyone for a Phd program, but rather for a counselor training program.)
-kiwi
***edit***
A few last things,
If you are uneasy about it, it will show. I have interviewed some people and when they talk about the situation their eyes kind of glaze over or they loose eye contact from me for the first time or they shift uncomfortably. The most successful interviewees I had thought a moment about the question and answered in a steady tone, steady eye contact, body language etc. They were obviously comfortable talking about the situation and had over come it.