Never sleep at a hotel the night before an early flight if the hotel is less than 20 minutes from the airport. Sleep at the airport hotel — the one physically connected to the terminal — even if it costs more, even if you have to walk longer, even if it looks charmless. The 20 minutes you save in the morning are not the point. The point is that you are one variable away from missing your flight, and that variable is transport.
Transport is the failure mode. Uber cancellations at 5am. Metro that unexpectedly does not run until 6:15. A taxi rank that is empty when you thought it would be full. All of these have happened to me. The two flights I saved were both because I was staying inside the terminal complex and could walk to check-in in seven minutes when everything else fell apart.
The airport hotels also have soundproofed windows, know what an early breakfast is, and often have direct check-in kiosks in the lobby. The vibes are worse than a boutique hotel. The reliability is 10x better. For any flight before 8am, this is now my default. The 40 extra euros are the cheapest travel insurance you will ever buy.