Forest of Dreams — C.L. Bevill

On one day everything was normal. The next morning billions of people had vanished, and new magical creatures had appeared, altering not only the Earth but everyone who woke up on that one day. Lulu survived the change, only to encounter far worse situations than she'd ever known before. Two years after a sea of dreams transformed everything, Lulu searches for “tech bubbles,” places where technology is still operational, and consequently useful to the survivors. What she discovers is that not all weapons from the past are nonfunctioning, and that the past is never truly dead. She will fight to save the new world and everyone she's come to love.

Forests of Dreams is book 3 in the Dreams series. Book 1 is Sea of Dreams. Book 2 is Mountains of Dreams.