I took it back in the 1980s. Didn't think that train still ran. It was a train like most of the others. We got into couchettes and went to sleep on the planks, at least I used to sleep on the trains. Poor DH never could. I always had colds the next day breathing the dusty air after overnight in the couchettes. It rocked and swayed, wheels screeched. Starting and stopping all night long. Lights coming in from stations, workers talking outside on the tracks, throwing mailbags into the mail cars. Had to change track size car-by-car at the border. There are certain sounds, rhythms, sensations, odors that are only on those old night trains. Took forever to get to Madrid.
We've happily used the TGV to Barcelona, but if you are healthy and sleep well, why not. I'm glad to see night trains disappear, but maybe everyone should try it some time.