Yesterday - after two days at home - we rushed to the hospital again. (Just to reveal the good ending: we didn't have to stay.)
Kalle was coughing so badly he started to cry. The crying caused more coughing, more phlegm. Breathing between the coughs became more and more difficult, he started to make terrible sounds while he was trying to suck in some air, his lips turned blue-ish...and we called 112 (Europe's 911). It looked like Kalle might choke every second and just stop breathing.
When the ambulance came they checked Kalle's oxygen level, which was surprisingly good, they sucked away some of the phlegm, drove him and me to the hospital. Kalle calmed down a bit, the doctors checked his lungs (sounded okay, just a lot of phlegm) and we were asked to decide whether we wanted to take him home or not.
So after a couple of hours we drove back home. Advice: If something like this happens again the only thing we can do is let Kalle inhale some of the med he is using anyway when he has a cold.
Let's just hope this incident was just a stupid coincidence and it will NOT happen again. It was pretty scary.