Anxiety disorders are complex and varied. Among them is a condition called obsessive-compulsive disorder, or OCD, and some experts believe hoarding to be located somewhere on the OCD spectrum. One of the things anxiety disorders, including OCD, have in common is that whatever coping mechanism someone chooses, the goal of that behavior is to exert control over one's life.
Taking control by clearing out someone's "junk" or calling the authorities or making a therapy appointment is not a great place to start (although it may come to that). This approach will only cause greater anxiety and therefore a more intense reliance on the coping mechanism -- in this case, hoarding. For each solution you feel might be beneficial, offer alternatives. For instance, professional help could be in the form of group therapy, support groups or individual therapy, and "getting rid of" the hoarded objects could mean donating them, throwing them out, or even moving them to a separate storage space for the time being, just to get them out of the bedroom.
Of course, storing the stuff somewhere else is not a long-term solution, and in many hoarding cases that might be just as terrifying as throwing the stuff in a Dumpster. In the end, if the problem involves health and/or safety concerns and your attempts at helping gently go nowhere, the only way to help might be to step in and take control of the situation.