I am German and yet on night flights I figured that the temperatures are way to hot on LH flights.
At home I sleep with open windows and the temperature in the sleeping room can easily fall down under 17 degrees. In summer we use a portable AC as well to cool down the room before we go to sleep. But we don't use it while we sleep. Too noisy and the constant air stream in the room is also annoying.
On the flights it is a bit of cultural issue. Europeans are not really used to ACs and prefer it a bit warmer. Hence the 22/23 degrees temperature.
At night the Europeans like it a bit cooler, but only when they sleep.
So while we sleep, those ladies who are keeping the watch or providing us some water every now and then, sit around in the galley reading magazines or chat.
When going to the bathrooms, I reckognized they always wear jackets or else over their blouses and they seem to freeze. So they increase the room temperature.
And this is why we all feel too warm and don't sleep well.
On top of it comes the massive meals and alcohol consumption on board. While we want to sleep our digestion is in full working mood. Creating a lot of energy. Another reason why we feel hot.
I don't eat anymore on board if I want to go to sleep real soon. Alcohol is also no option for me. It is an urban legend that a beer or glass of wine let's you sleep better.
By the way, at home you also don't have a big meal 10 minutes before you go to sleep. Think about it.