I’ve been trying (with no success) to find a story I read on the internet about a decade ago about a man that either falls asleep or just decides to travel to the end of the line on the train and ends up at the depot. Whilst there he boards a train to return to where he came from, but finds out that the train he is on takes him through an alien world/another dimension.
He then tries to get back to the depot but ends up at a different one and gets on a different train that ends up taking him to another world/dimension.
He then travels on the trains trying to find his way home for some time (maybe even years?) to the point that he starts transforming into something else and by the time he reaches back to where he started, he can no longer be seen by the inhabitants of earth. (Very hazy on this last bit so easily could have imagined the last bit, but the rest is definitely well remembered!)