What is it called, and are there people like me ?

Everyday, it's like I have a quota of words I speak, and then I can't say anything anymore.
For example, if I'm really talkative in the morning, I'll be calm and quiet the afternoon. Sometimes my friends notice and be Like '' did something happen ? Is something wrong ? ''. And I'm perfectly fine, I just don't feel like talking, I only feel like daydreaming and watching clouds. And I'm not particularly shy or something, I just talk a lot and smile and laugh when I'm on the talking part.
People think I'm weird and bipolar, but maybe I'm just lunatic or something.
Is there an adjective to describe this ?