Crashing

This morning I woke up groggy. I went to sleep finally around 2am, kept waking up, had very odd dreams and was woken up at 7:11am by a small child needing me to help her downstairs.
Despite that, my mood wasn't terrible. I went back to bed and dozed for a while, but again kept getting woken up by the kids. Which of course I cant blame them as they're younger and cant get they're own cereal etc.
I got up, sorted my coffee and stuff, had breakfast, did some housework and listened/read about Liverpool beating Everton 2-0. And I was tired, but fine.
Then all of a sudden, around an hour or so ago, I just suddenly felt really down. (I don't want to use the word depressed, because I think that should be used in its correct context.) I have no reason for this mood crash that I can think of. I didn't have an argument, nothing happened to cause this. I was just, all of a sudden, wanting to go and lie on my bed, curl up into a ball, and cry. Maybe if I did that I would feel better. But I cant.
Those small people that woke me up this morning are still around playing. I cant just go have a little breakdown because it would upset them terribly. I simply don't have the time.
I'm trying to think of what might be making me feel this way. What it is that's not letting me be happy. These mood crashes come so regularly to me now but then I seem to lighten up just as quickly. This does worry me a little but I know that I'm not happy with my life the way it is.
I'm not happy with where I live, although I am grateful that I actually have somewhere to live. I'm not happy about being alone, except I would rather be alone and unhappy, than be with unhappy with someone. I'm not happy with myself, the way I look and the way I feel about that. There are other things that I have to work on to change about myself, my attitude and my outlook, I know that. But would my emotions not give me a bit of a break in the meantime?
There is one thing that keeps popping into my mind but that's only from today, it wouldn't really explain previous mood crashes. October 30th will be the 17th anniversary of my dad dying. Hes been gone 3 years longer than I got to be with him, and even this much later, it hurts more than anything ever has. I miss him more now than ever and I wish he was still here. I need him.
But I cant blame this on that, it was so long ago. Yeah I miss him, but I cant let that affect me so much. I don't know, maybe I never really got over it.
I don't know about much of this right now to be honest.
All I want to do now is to find some really sad film and cry the mood out.
I hope it helps because this is exhausting me.