I, myself, just got out of the hospital where I was in the "high functioning" ward. One of the program specialists made the comment that high functioning depressives can actually be the most dangerous.
Her example was in the hospital setting. You take someone from one of the lower functioning wards and place them in front of the doctor, and the doctor decides to put them on medication. The person might just sit back and say, "okay." But with a high functioning depressed person, they are more aware of what is going on, their illness, their cognitive operations, etc, and will sit there and argue against the med, even if it's against their own best interest.