Guide to gyro and accelerometer with Arduino including Kalman filtering

Lauszus:
Is that both with the Kalman- and Complementary filter?

yup Kalman filter is giving much better results, so I have switched to that now.
One more thing I noticed, the moment X-axis angle starts to approach 90 degree and onwards, Y-axis angle suddenly goes crazy. And same is the case with X-axis angle when Y-axis starts to get near to 90 degree.

Is that due to my IMU or you are experiencing the simillar results with yours?