Is cardiomyopathy dangerous to have?

Depends. It depends on the cause and if there are reversible factors. If it is severe and/or progressive, getting to a heart failure specialist is critical, but any cardiomyopathy should have at least a full cardiology consultation to assess the possible treatment paths appropriate for the circumstances.
Yes. It shortens life expectancy so, in that regard, it's dangerous. Sometimes cardiomyopathy is reversible and it's always treatable. There has been a lot of progress in treatment and prognosis in the last 25 years.