It takes quite a while for a plant to react to adverse conditions (unless they are extreme). It is likely that your moving it to better light and its subsequent decline was simply coincidental, not cause-and-effect. It is hard to imagine that you could provide too much light for it in Denmark in March/April!
To help you determine the soil moisture content, I suggest you remove the loose soil on the surface. It serves no purpose, but it does dry out quickly and misleads you about the soil around the roots. Then, allow the top inch of soil to dry before waterings. That drying out is what will allow oxygen into the root zone. I cannot tell you how much to add except that you should add enough water so that a bit drips through the drain holes.
It will take a while before you see any improvement after you increase the light and water as I described, so be patient.