vaginapagina | Self-lubrication

Hey VP! I've looked through all relevant tagged posts and I don't think anyone's covered my question. If I'm wrong, just point me to the right post and delete this! :) Anyway I'm wondering about my vagina's self-lubrication process. Often during sex no matter how turned on I am I just don't get physically wet enough and we have to use lube, which is fine enough. But I know I can physically produce the stuff because sometimes I feel, uh, thoroughly lubricated at completely irrelevant times, when I'm not turned on and just going about my day. Is there any way to predict/understand this or is it just something that happens?

Thanks for any information.