Did the Euro crisis make you feel unhappy? What about the earthquake in Turkey? The Bristol murder case? The weather?
Ever felt really good one moment and the next you've been plunged into the depths of despair? It can happen for the simplest of reasons. What if a friend just told you they'd been given a massive pay rise? Chances are that you won't share their joy - it will probably throw you into a depression.
Research quoted in Richard Leyard's book, Happiness: Lessons from a new science, shows that our happiness with income is not based so much on what we earn but how much we earn relative to the people against whom we compare ourselves.
Or you might feel beleaguered by endless news about disasters. Again, research by Daniel Kahneman shows that we are affected by the availability of information. If our minds are saturated with one type of information - disasters, for example - it will both affect how we feel and what we do.
After 9/11 many people stopped flying. In the UK, after the Paddington rail disaster, commuters eschewed the train and took to the road.
Take a walk in the high street. If you go to an affluent area where people dress well and walk purposefully, your mood can be lifted. If the area is poorer, you will find that people dress less well and may walk more slowly, ambling and wandering. That too could affect your mood.
Our friends affect us too. Christakis and Fowler's book, Connected, asserts that not only will our friends affect our moods but they can directly affect our behaviour. If our friends get fat, so will we. If they get divorced, watch out for your marriage. Scary stuff.
But we're also affected by people we don't know. When others drop litter it can give us tacit permission to do so. When others cry, we feel able to cry too. The death of Princess Diana showed how easily we can get caught up in others' grief.
There's more: apparently we inherit over 50% of our behaviours from our parents. So if our parents were prone to mood swings and sudden outbursts or rants, we may well find ourselves doing the same. (There's your excuse if you now rant at the TV).
And if all this wasn't enough, there are advertisers out there spending billions of pounds trying to persuade us that we are inadequate, unhappy, weak, unsexy, boring, desperate, stodgy, unattractive without whatever they are selling. Buy these things and all will be well.
So if you're feeling happy right now, close your eyes, don't look out the window, don't turn on the TV, don't listen to the radio, don't ask why your friend is so happy because it could all change.
This might make it feel as if we are all just corks bobbing about on the waves of others' moods and behaviour. And to a degree we are.
So what can we do about it?
Start by understanding what affects your mood. Spend a little time with yourself (getting away from the TV won't do you any harm anyway) and think about what affects your feelings throughout the day.
You could even keep a mood diary. Set out a score from 0 - 10 (where 10 is ecstatic) in one column and write alongside each score (which you could judge hourly) what salient things in your mind are really affecting the way you feel.
Once you have identified the primary influences on your mental state, decide what you can do about them. Some things you can change. You don't need to ask your friends whether they've had a pay rise. You don't need to go out when it's raining if that makes you feel bad. But you can't do much about your parents, especially if they're down-in-the-mouth folks.
Find out more about the kinds of things that make you feel better. That might change at various points in the day. When I'm writing under pressure, I find that high energy music works really well - early Nirvana, any Led Zeppelin. When I need time to think, Mahler usually delivers. But if I'm agitated, then any music gets in the way.
Look at the input that's coming into your brain. If your BlackBerry stresses you out, put it away. (The world will not collapse if you don't read your emails). If the news depresses you, don't watch it. It's not a real reflection of the world anyway but the world refracted through journalists' values. See Bad News.
The more you know yourself, the more likely you are to understand what makes you tick and give you a sense of what you should and should do during the day to secure your happiness irrespective of the horrible things that will happen whether we like it or not.
Besides, simply knowing yourself and being clear about who and what you are, could well make you happier anyway.
Follow Mark Fletcher-Brown on Twitter: www.twitter.com/morque