If, physically, you're healthy, then yes, the problem is anxiety.
Take time to consider any significant changes or problems you need to be managing more than you are.
Perhaps it's not one big change or problem, but an accumulation of small ones.
For instance, maybe you've been taking on more and more duties at work, and you haven't been properly compensated. You're doing it to be a "good employee" without complaining, not realizing you'll get more respect if you speak up.
Just spit-balling here.