Explaining the temporary condition can help so people know they aren't alone (knowing you are one of millions who have had the same exact thought processes is a wake up call).
Mentioning the processes can be caused by certain foods and medications in some people seems like a good idea too. ("Feeling suicidal? Did you just eat twelve pancakes with half a gallon of syrup? All the sugars have screwed you up for a while. Sleep it off. Did you just start a new antibiotic and now you want to jump off a bridge? Sleep it off. Call your doctor to get different meds. Your brain will reset.")
My biggest mistake was postponing the decision to talk to somebody for several months out of false pride, thinking I'm able to handle it myself.
For me, two things help: reminding myself nothing matters as much as I think it matters and setting a medium-term goal. Our decisions can be anything and it's fine. The world--universe--is a big place. Take risks. Nothing worthwhile is judging you. So, build something new. Meet people. If you make a fool of yourself, it doesn't matter at all. Let other people wonder why you're impervious to their hostility. You've seen the truth. In the grand scheme of things, we can't even be seen: http://en.wikipedia.org/wiki/Hubble_Deep_Field
The world is yours to do with as you please. Take advantage of it.
Problem here is that when you finally meet someone to chat with, you're probably way too desperate to get that feeling that someone cares about you. It might be hard not to talk only about your self. That's how it goes for me at least. And people smell that despair far away. My advice is: remember to force yourself to ask questions when you chat.
Internet relay chat is good place to rehearse social interaction, but it's bad supplement in the long run.
Having been in your situation, the things I found helpful for a quick fix were exercise and food. It doesn't matter how much or what. If I am in a slump and feeling like it is all too much I force myself to do some exercise. A chin-up, a push-up, go for a run or a swim. If I am feeling really bad I will make myself do one push-up, on my knees. or just kneel on the floor and do a negative repetition. That's usually enough to get me started on doing something. Then I will go and eat some food. Or more likely, go to the shops and buy some food to cook. Then eat something. For me doing a little bit of exercise and then eating often makes enough of a difference that my misery is manageable.
There is some evidence that exercise is helpful for others in dealing with depression, e.g. [1] (A review paper) Anecdotally, this seems particularly the case if you are at all ADHD.
Long term I agree with all the other posts pointing out that seeking professional treatment is the best option. The pride factor was a huge problem for me and still is. I treat it like research. Psychiatrists and Psychologists, are experts in there field who I pay to explain options for treatment an methods for assessment and monitoring. Thankfully this has only happened once, but if they can't explain the different options and why the course of action they recommend is the best I find a different doctor.
I'm not an expert, but try going to a public place, maybe a museum where you'll be forced to interact at least with the ticket guy. Or even a mall, and maybe ask some questions about some product ("does it come in blue?"). I'm not saying it's a solution, but it might get you an encouraging quick fix for some human interaction, to give you some energy to do other stuff.
- Journalism codes for reporting on matters related to suicide: http://en.wikipedia.org/wiki/Copycat_suicide#Journalism_code...
- Social proof model for explaining copycat suicides: http://en.wikipedia.org/wiki/Copycat_suicide#Social_proof_mo...
- Cialdini's book, Influence: the psychology of persuasion, references some scientific studies on this subject: http://en.wikipedia.org/wiki/Copycat_suicide#cite_note-isbn0...