Here is the information as I was given it:
Ultralite Soleil: Hi all, there have been many questions about the fatigue in TE3000. Here is the upshot: Fatigue builds up in your fleet from too much trade activity. It only affects you after quite a long time of playing the game in a single day. If you are affected, you will see "(Fatigue)" at the bottom of your ACCTS tab. It lowers your fleet efficiency which affects your income. It resets back to zero once per day. You don't have to do anything. It resets whether you are online or off.
If you play the game for too long (12 hours of continual play) a "Fatigue" Feature kicks in and your profits start to rapidly decrease. Perhaps working as an anti bot feature. You will notice the fatigue in your accounting section.
If you see this immediately detach your HUD or log off because it will start to suck up your profits. It eats your profits at an increasing rate and eventually you will start to lose credits overall so its better to detach sooner than later.
THE FATIGUE RESETS ONCE PER DAY ACCORDING TO ULTRA. IF YOU START SUFFERING FROM FATIGUE, THE ANSWER IS TO TAKE IT OFF AND WAIT FOR IT TO RESET. IF YOU CONTINUE, YOUR INCOME WILL DECREASE TO 0 cr. WHEN THAT ONCE PER DAY IS, WE DO NOT KNOW. FATIGUE GENERALLY SETS IN AFTER 12 HOURS OF CONTINUAL PLAY.