Air interdiction!

[Aetius]

From PzCampaigns manual:

Air Interdiction

"As units move on the map in Travel or Rail Mode, there is a chance that their movement will be Interdicted by enemy air units. This probability is based on Parameter data per side (see the Parameter Data Dialog in the Main Program). The probability is based on the total number of units in Travel or Rail Mode in the hex being moved into. The probability is modified by any terrain modifier of the hex being moved into. The probability is half during Dawn and Dusk turns. If Interdiction occurs, then an Air Strike occurs against a unit in the target hex using an air unit that is representative of the type of air unit available to the enemy side. However, this air strike does not count against the air units available by the enemy. Note in addition, that movement by units in Deployed Mode into hexes occupied by units in Travel or Rail Mode can also trigger an interdiction attack against the units in Travel or Rail Mode."

So, you have a few tips there that can decrease the possibility of interdiction even in daylight: move through defensible terrain, avoid the open and have no more than one unit in a stack.
If you have to move at night only don't worry about night fatigue; you will have plenty of time to recover during daytime.

Rui