What to do when feeling blue about what usually makes me feel yellow

What do you do when what usually provides you with the most happiness becomes one of your biggest frustrations?

Here's my dilemma.

I love sports. I enjoy watching sports, I love to play sports. I regularly play ultimate [frisbee] a couple of times a week and volleyball once a week.

I spend a lot of time looking forward to games of any sport. I smile more talking about and playing sports than just about any other time. Sports energize me.

Usually.

Lately, that is not the case and it's thrown me for a loop. Last week's ultimate games were so frustrating I would've walked off the field mid-game if it wouldn't have drawn attention to me and my bad attitude. Last night I didn't want to go to my volleyball game. When I was playing, I would've been fine for the match to be over at any point. Afterward, I didn't feel like talking about how we played.

I'm apathetic about playing but also quick to anger when I do play. If someone makes 2 stupid plays in a row (mental mistakes, not just missing something) I get angry at them. When two people do it, forget it, I feel like stomping off the field. The anger I felt last week at myself and other players was so great that I would rather not play today.

This is coming from a woman who plays even when she has a migraine. This is coming from a woman who has driven 30 minutes home and 30 minutes back to work (during the work day and knowing the time would have to be made up in the evening) when she forgot clothes to play in. This is coming from a woman who knows what each player needs to hear, in order to decide to play on a day that they're not sure if they want to come out or not, so that she can get enough people for a game. This is coming from a woman who knows that she should get home to her family but instead stays for an extra hour of volleyball because it's impossible to pass up a chance to play doubles.

All my life I've had what people might call a "bad attitude" about things like my performance in sporting events. When I was young, I competed in gymnastics and I recall a distinct event when, during practice, I used a very serious curse word at my coach when I was 9 years old.

Over the past 10 years, I've gotten away from some of my more childish behaviors regarding sports, in particular. Now it seems as though I'm a kid again, unable to control her temper, wanting to stomp off in a huff.

Where did this come from? Why is it showing up now? How do I get rid of it???