A sensation of pain
A diminished or non-existent ability to experience joy or happiness, a tendency to dwell on negative emotions, continued sensations of helplessness and hopelessness, a reduced sex drive and thoughts of suicide.
These are all symptoms of depression, but just as strongly, they're the side effects of supporting Manchester United. You might replace Manchester United with the name of most big sides and the comparison would hold, but Manchester United have a particular position in football which exposes their fans to the most suffering. If you know a Manchester United fan, do not envy the success of the team. No, feel their pain.
When Manchester United defeat Wolves, it's unremarkable. Nobody really cares. Both sets of fans go to watch the match expecting a rout, and more often than not that's what they see. The possibility of a small team beating Manchester United is so unlikely that often the smaller team gives up ahead of time, playing a second-string XI in order to conserve resources to use in a more balanced match. The three points won by United will be noted in the most perfunctory manner by most of the press. It can hold no shock value.
So when victory becomes cursory and routine, the novelty wears off. A victory against Tottenham? No great shakes. Beating Blackburn 7-1? To be expected. If your team played games that held no meaning for 95% of the season, mere obstacles rather than challenges, then you to would experience the same dulled response.
When United lose unexpectedly, though, the defeat has far greater impact than on the average supporter. They will experience draws and defeats on a regular basis. Inevitably, the sensation of pain will become familiar. For Manchester United fans, defeat is such a shock to the system that the pain is sharper and more poignant. Anybody with a sense of empathy will feel sorrow on the behalf of a Manchester United fan experiencing one of the three or four defeats they can expect in a year.
It's not just victory that means nothing, it's most signings. Should Manchester United end their business now, they will have bought David de Gea, a keeper of fantastic potential, Phil Jones, the most talented English young centre-back available this summer and Ashley Young, a player of proven ability in the Premier League.
All potentially great buys, but the summer is a dark time. Why? Because Wesley Sneijder might reject them. The same has already gone for Samir Nasri, who joined rivals City. Once you're used to such relentless acquisition, the transfer conveyor belt becomes numbing because it is not all conclusive - a Manchester United fan is always missing out on something. Relentless success can only emphasise the negative.
Because the stakes are so high - a season is a success only if the league or Champions League is brought home - a victory the following Saturday is only slight succour. For a Manchester United fan, negative emotions last the full year, until the Premier League is reclaimed. Imagine the awful period of 2004-2006 where Manchester United went without domestic or European success. The moping period was inhumanely painful.
Manchester United are the biggest side in Britain. In terms of fans, they may well be the biggest side in the world. So, the contribution from each fan is diluted by the sheer weight of their peers. If one fan is unhappy, he will be drowned out by the others. In light of the Glazer scandal, this highlights one of the problems of supporting Manchester United. Just as in depression, you feel insignificant.
When dissident supporters gave up their season tickets in protest at the debt leveraging and ticket price increases, there was always a new supporter ready to take over the subscription. Despite the valid protest any disenchanted fan was making by withholding financial support, there would be another fan happy to pay a higher price to get a seat at Old Trafford. If depression engenders a sense of hopelessness, then making a protest that's nothing more than pyrrhic has a similar effect.
Most teams have one great rival. Tottenham have Arsenal, Barcelona have Real Madrid. Support Manchester United, and it's far worse. By virtue of history and geography, it's not that easy. You can make a case that in the last decade alone, Manchester United have established or continued bitter enmity with Liverpool, Arsenal, Chelsea and Manchester City.
Upon each game rests real hatred. The battle of league titles and European Cups continues with Liverpool as the scores close on parity. Arsenal have 'Pizzagate', title run-ins and mutual aggression dating back to the nineties.
Chelsea were the nouveau riche who came close to knocking Manchester United off their own particular perch as the dominant force in England. Manchester City are trying the same deal, with the added frisson of a history of location and envy. Until the Dubai takeover, Mike Summerbee had been the one man to keep it going, but now you have regular dispute over the same trophies and players. So many enemies engender a sense of persecution, another symptom of depression.
While most of the games don't matter to a Manchester United fan, the ones that do are played at a fever pitch. The sheer height of emotion must push a significant number of people to the brink of a serious life decision if they lose.
Helplessness, hopelessness, negative feeling overtaking your life. While you might consider winning the Premier League with a dysfunctional squad a great relief, all it does when you're suffering from Manchester United is give you 'The Fear' as you fret for next season.
• Alexander Netherton is co-editor of Surreal Football.