It's hard to interpret dreams thrid party. There's a lot of questions that would need to be known. Is your friend metnally ill? Are they taking any medications psychiatric or otherwise? How old are they?

All characters in the dream are personifications of the dreamer....each represents a differetn part of the dreamer's personality. We see here that the dreamer is getting on a train, which implies that there's a great deal of travel ahead in the dream. This is a "moving forward" dream, and I think it's addressing a subtle subconscious fear.

The train and the implied travel is symbolic of moving forward in life. Change is constant, and all we can do is adapt and get on with things. There is this looking back onto classmates, but we also see that everyone is wearing masks. This tells me that these expressions of the dreamer's different personality traits comes with different masks of sorts. Basically, depending on who they're with and what they're doing, they act differently. This isn't uncommon at all, but as life goes on our masks have to be cast aside in lieu of adapting to new circumstances. This is the dreamer facing a fear...the fear that the masks will remain, but the "old dreamer" (the way the dreamer was in days gone by) will melt away into nothing. It's the old "If I'm not who I was, then who am I now?"

That this is a recurring nightmare tells me that the dreamer is anticipating a great change and doesn't want to face the transition into this new part of life.