I, just like anyone else, go through ups and downs. At times, I'm sad. I think more often than not, I'm happy. I can't be happy all the time though - the sad times are inevitable. I've started to learn that what is important is how you deal with those situations - the ones where you're sad, depressed, down - how you deal with them is crucial to get back to your positive, happy state.
It's important to recognize when you don't feel like yourself. I'm someone who loves to have a positive outlook - I want to interact and smile and laugh. I want to enjoy day to day activities and smile when I see other happy people. When I see myself approaching things differently than this, I know something is up. You need to recognize you're feeling off because it's the first step to feeling like your normal self again.
Once you've recognized it, ask yourself why.
Why am I feeling down?
Do I have a lot of external stressors?
Am I not making the progress I want to be making?
Am I creating a problem in my head that isn't even real?
Is this related to a past decision I made?
Once you've recognized why you feel off, it's easier to get back on track. The recognition lets you develop a plan of action to work through your tough time. It gives you something to talk about with others.
The point I want to drive home is this - ALWAYS take action when you're down. You can't stay that way. It's won't let you live your best life. Your greatest and most significant achievements happen when you're inspired and driven. It's difficult to pick yourself up sometimes, but you can always find the inner strength to do it. If you want to be happier and have a more positive outlook on things, dig deep and find strength. The strength is there - you just need to find it. Remember how enjoyable life is when you're happy and use that as motivation to get back to a positive state of mind.
And remember - you will get through it. Life is about balance. The bad times make the good ones so much sweeter.