Stop trying to “fill time.” You are not useless, not lost, not slothful if you choose to simply “chill out.” There’s nothing at all wrong with simply engaging in introspection, fantasy, or speculation. No one is paying you to be constantly in action, or “working the phones,” or attending meetings.
Mindset: Free time is a blessing, not money burning a hole in your pocket to be spent. Try emptying your mind and giving yourself time to rejoice in life.