The 33-year-old "Toxic" hitmaker has been using a special application for 20 minutes every day to learn to relax and banish her anxiety, reported Contactmusic.
"Britney has always struggled with anxiety. Learning to meditate, relax her mind and body and have happy thoughts has made her change dramatically.
"She lives in the moment more and, instead of moaning about working out, she looks forward to it, revealing the endorphins make her think happy thoughts," a source said.
Spears, who split from boyfriend Charlie Ebersol recently after eight months of dating, is feeling "happier than ever."
"She's feeling full of energy and seems happier than she's been in a while," the source said.