These are the ones who are clinically depressed. The ones who, as did Paul recently, request a chat after tutorial and sit, sobbing, able to account neither for the origins nor the depth of their despair.
When such misery defies explanation from its victim, where else to turn? A good place to start would be the helpline number given at the end of each programme in the three-part television series A Living Hell.
An inquiry into the origins, nature and treatment of depression, the series should prove invaluable not only to psychology teachers but also the rest of us. For these days, alas, there seem to be more and more students like Paul.
Clinical depression can strike anyone at any time, but some seem more prone than others. For presenter and former depressive Lewis Wolpert, the answer lies in an uneven blend of nature and nurture. The "absolute hell" that is the life of one of the depressives interviewed in the opening programme was largely put down to a DNA pattern. Studies of twins bolstered the biological emphasis, with depressive traits more prevalent in identical than non-identical twins. Careful nurturing, said one researcher, does make a difference; but it soon became clear that there were more DNA than TLC links in Wolpert's causal chain.
A memorable example in programme two showed why. Photographs of Beryl Dawson taken at the height of her depression in 1994 showed her as acned, obese and expressionless.
The problem was a tiny tumour on Beryl's lung which, when removed, stemmed what had been an excessive production of the stress hormone cortisol. The contrast between Beryl before and after treatment made one gasp.
Aimee Middlemiss also found relief in drugs, though not before dropping out of university. Now, she knows what to do: "Go to the doctor's, get the pills, and go find someone to talk to."
Like Aimee, Wolpert puts much faith in time and tablets. The trouble is that doctors have more of the second than the first. Where more time should come from is a political question that Wolpert seems unlikely to ask.
In the end what Wolpert offers most is hope, even if it is the kind to be taken three times a day after meals. For that, at least, he should be thanked.
A Living Hell, March 17, BBC2, 11.20-11.55pm. Free confidential helpline (0800-888809) afterwards until 2am, and 9am-3pm next day. Useful information is available on web site: www.bbc.co.ukeducation