A video that had a million visits has stopped having practically visits, How to Analyze?

I have a video with more than one million visits but I really do not have much idea of why you have stopped having visits.
Could someone give me some tips to be able to analyze better because this can be happening?
Does anyone have any explanation or something similar has happened?

Thank you all information, if you have some source of training where you can spread to analyze this kind of thing I appreciate it iguly

may be it got many reports?
Or does the video become age restricted?

When it hapenned? I can tell you that I was getting good amount of views on new channel...All of my videos were doing good...then I upload new video about bitcoins..Suddenly ALL my video views dropped about 80%....I dont know why, But I think it was because of this bitcoins video, it was not any kinds of spam etc just guides....