Live color customizer "frozen"

I have been using the customizer with high-end theme (WP), perhaps a bit too excitedly switching between that and the set color schemes (e.g. minimal purple) , experimenting and trying to get the right look.
Now when I access the customizer the tab says “Customize: Loading.” The menu is blank; no title, nav bars, color choices…nothing; except for the words “You are customizing Razz Popo,” and the “save and publish” button.
And I was so close to finishing the site design. I want my customizer back. Any assistance will be appreciated, Also, I am a novice with tech stuff so you may need to explain as if to a child.