In the end...

...I thought better of it and booked a bed in a hostel in Frankfurt. Sure, I could've just spent the night in some club till it was time to take the 5:00 AM train, and I would actually have to wait an hour less because daylight saving time starts just on the night between the 27th and 28th, but I found this hostel near the station and thought I could spent an extra 18€ to get some proper sleep. So I won't have to worry about falling asleep and missing my station when I have to change train. Besides, I will have to work the next day and I don't want to go to the office feeling like a zombie.

Now I just need to buy train tickets. I'd thought of simply going to the station and ask around like I did when I went to Hamburg in December, but I guess finding someone going from Berlin to Frankfurt isn't so easy as finding someone going to Hamburg, and I don't wanna push my luck. I'll just buy a Schönes-Wochenende-Ticket myself.

This is gonna be one hell of a birthday.