Tal,

Wasn't really a guess. When someone does things that don't make sense or behavior changes for no good reason, or a whole host of other strange symptoms---two of the first explanations to consider should be drugs and alcohol.
I could have saved myself a lot of misery over my lifetime if I had realized that fact a lot earlier in my personal life and my work life. I put a lot of effort into trying to figure out how to get a best friend, a son, and many employees back on track, never even considering drugs and alcohol as the cause for behavior that didn't make sense. It is much more prevalent than I had any idea it is, early death among alcoholics and drug users is much more common than most of us realize, and those addicted (or dependent) are not the same people we thought we knew. These problems are certainly not the only possible causes of strange behavior but it should always be considered (or ruled out), no matter how remote a possibility it seems to be.