How dangerous is it for your health if you regularly work from 6 pm to 5 am? i was told it raises several risks for diseases, even if you sleep 8 hours after your shift?

There is some risk. You may be able to mitigate the risk through healthy eating habits and regular exercise. Visit this site for info: https://www.nih.gov/news-events/nih-research-matters/daytime-meals-may-reduce-health-risks-night-shift-work#:~:text=Night%20shift%20work%20disrupts%20the,to%20process%20sugar%2C%20or%20glucose.

An 11 hour shift is a tedious work task. I really depends on the mental and or physical aspects of your job. If you can get a little rest during your shift, it would be helpful. If not too tired after work, go to gym for a workout, or before next shift. Drink lots of water, have a healthy diet, no smoking, and cut back on coffee, tea instead. Diseases come from unhealthy social and lifestyle.