I got an email today with suggestions of people to follow, including my former therapist. This was a little surprising because he only has 13 followers and follows 5 people. My only guess is this information came from email and browsing behavior that was collected and sold to twitter? Does anyone have a good explanation?
Your therapist probably gave permission for Twitter to scan their phone's or computer's contacts and it found your email. Then it recommended them to you. My phone's notification bar had an offer from Twitter to help me find more friends this way just this morning.
I see, this sounds very likely. It seems like this is irresponsible on the part of the therapist to essentially disclose a patient list to a third party. Do you know if there is any kind of legislation about this?
I am not a lawyer and this is not legal advice. But this is very unprofessional from the therapist side. You perhaps should contact your therapist as soon as possible and let him/her know that there is a breach of trust. Also read about HIPAA(Health Insurance Portability and Accountability Act).
This is why docs should not participate in "social media" that require or recommend registration using real names. It is difficult to fully compartmentalize one's life to the degree required (ie, if you ever spoke to a doc on his cellphone your name may be in the contact list). I'm sure some professionals (docs) want to use Twitter or Facebook as advertising, but there are real security risks, as this situation illustrates.
I would suggest you let your therapist know what happened - he (?she) may be unaware of what happened and he/she may want to take action to prevent repetition.