If you’re American that’s called daydreaming at work, so lock in and get back to work you thieving degenerate! Anywhere else? A sign of impending burnout, or an indication you are not finding your work rewarding.
Exercise, drink water, eat clean, prioritize sleep, and find a creative outlet. Maybe take a day off here and there to visit a park or take a long drive. Connect with your friends and loved ones more often.