Is my Espruino sleeping?

As @AkosLukacs says that's most likely the problem.

Other things to watch out for:

• Have you tried using a different wall adaptor? Some see that very little power is drawn by the device and then try and go into a 'sleep' mode.
  
• Are you using setDeepSleep? If so I'd remove it for now - setDeepSleep will be ignored when connected to USB, but when disconnected it'll take effect and if you have a WiFi connection open it may interfere