Why does Cortana come and go?

[Windows Central Question]

I have had Win 10 for over a week. Cortana operated well for two days, then stopped.(the voice part) I searched the web for answers then I troubleshooted all the majors: microphone settings, volume, etc. Then after three or four days Cortana came back for a couple days and went away again this morning. I have done nothing major to my computer nor have I messed with settings. Are vacation days written into her contract? Seriously, I'd like to know what is going on here.