For any next time, maybe rehearse what you will say in any such case;

• Identify yourself.
• Explain you’re a medical professional.
• Inform them you wish to inspect the well-being of the person in question.

As people before me have indicated – this might open up the conversation, even though the officers in question might (or might not be) proverbial ‘dicks’.

If you’ve identified yourself as such, any and all force after that will be very hard to justify to a court or commanding officer.

That said, I have witnessed in the Netherlands that officers seem to act on mentally unstable people as ‘being on drugs’, which is a fair assumption, as I live in a large city and there are in fact many people on illegal substances after a certain time of night, in certain parts of town. – Even though I disagree with the force you discribe as a first response, I can understand where the reaction is coming from. (If 95% of people are in fact on drugs or so on, the response will be as such, since 95% of times the officers will have engaged in an appropriate manner).

I think there lies an opportunity in teaching / tutoring police officers to recognize the distinction between the two. Since you care a lot about the subject, maybe see about any programmes that set out to inform law enforcement personnel? (Or maybe find like minded people and start such a thing yourself. – Every journey begins with a first step, and all :))