Depression can vary from one person to another; they may exhibit all the behaviour, or just one aspect of it, and so it's important to know the signs and symptoms of depression and what to watch out for.
Bridget O'Connell, head of information at mental health charity Mind, told the Huffington Post UK what to watch out for, and gave some advice on what to do if you do think you, or someone you know, is depressed (scroll to after slideshow).
"Those are the sorts of things to look out for," Bridget explains. "The pressure isn't on you as a friend to decide what to do - it's just about keeping an eye out and offering support and help."
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So what if you do think you house mate, course colleague or friend is depressed?
"Talk to the person and listen to them. Some of the stuff they say may be hard to hear. Some people who are depressed might self harm or be thinking about taking their own life. Be prepared for that - it may be tough to hear. But it's about asking the questions and listening to the answers.
"If someone used to go out a lot and now they're not, just ask things like 'if we go out tonight, where would you be comfortable?'. Don't put pressure on them just give them a choice. It's about helping them come up with solutions to help themselves.
"It's that reassurance too: 'If you need to talk I'm here, you're not the only one who feels like this.' And then finding out from the university what support services they have - helplines, counselling services."
Bridget continues: "Also be prepared, if someone is thinking about killing themselves or harming themselves, that you're able to talk to them about getting an emergency GP appointment. Or, if they do need to go to hospital, then it is appropriate to call an ambulance. It's ok to ask them if they'd like an ambulance, if they'd like to be somewhere safe.
"Be prepared to take action. I'm not saying everyone who is depressed is thinking about taking their life but I'm just preparing you for the worst. For many people, having someone there, someone who is offering to listen, is the most important step and will help them seek advice. You will hopefully get your friend or flatmate back again and living their life the way they should be."
Useful websites and helplines:
Samaritans, open 24 hours a day, on 08457 90 90 90
Mind, open Monday to Friday, 9am-6pm on 0300 123 3393
Students Against Depression, a website by students, for students.
HopeLine runs a confidential advice helpline if you are a young person at risk of suicide or are worried about a young person at risk of suicide. Mon-Fri 10-5pm and 7pm-10pm. Weekends 2pm-5pm on 0800 068 41 41
Mental Wealth UK To join the community or launch a student group contact the charity on home@mentalwealthuk.com