... not from the ride as much as the concentration that was required not to wipe out everyone
... sounds like you were riding "in close formation"? Giving a lot more space to each other would let you all relax a bit? Just a thought.
Does it get it easier with practice?
Yes ... and definitely has its own distinct pleasures

.
- riding along with a ghostly barn owl tracking you, 20 feet off your shoulder?
- bats flitting around?
- animals of the night, the ones that pop their heads out of the grass verge ... stop, stare, and wonder what on earth's approaching?
- night-time flower smells?
- a clear, cloudless, moonless sky?
- moonlight?
- riding in a tiny cocoon of light, quite alone, in a different world entirely?
- etc, etc.
Oooh - and riding up long hills is SOOOO much easier at night. [True. Not tongue in cheek.

]
[edited to add ...
I forgot the simple enjoyment of riding without front lights on a clear moonlit night.
AND NOOOOOO! Don't go there! It's just for riding a quiet bridleway or similar. Or in the wee small hours, when you can see the VERY rare motor vehicle approaching from a very long way off. And it has its own, slow magic.]
[editing again, to add
- the calls of the first skirling curlews to waken, just before sunrise;
- deer - startled ... but puzzled, dead still, and watching you from the path-side, in the hour after dawn :-)