Something that I've never found out through years of play.

[Mr Grumpy]

The answer to your question is that any action taken by your units on your turn or in reaction to your opponents turn will prevent your unit recovering from fatigue, you need to pull the unit out of the front line and out of your opponents LOS. 

Remember that fatigue recovery is doubled on a night turn so try not to move at night if possible!

It took me a while to realise that by not breaking my battalions down how much fatigue I could prevent accumulating although I realise that it is not always possible to keep battalions combined.

Personally I think even with the night fatigue rule being used it is too easy to fight 24/7 in the PzC series, I like the fact that the night movement disruption rule in FWWC forces players to rest at night.