If a cop wanted a reason, they have no need to have you provide one.
Police don't get aggressive for shits and giggles. They know it could escalate into something much more serious. Police are trained to do a certain thing a certain way, and if you don't comply, you are interfering with their procedures which makes it more dangerous for them and you.
If a police officer told me to get on the ground, I would simply do so. If he wanted to put the cuffs on me, I would comply even though I did nothing wrong. If you are going to challenge authority, you don't do it on the street. After the matter settles down, you can use the many avenues to resolve your issues afterwards.
One time I got pulled over in a weigh station and they wanted to checkout my truck. They were yelling at me like drill sergeants in the Marines. The one officer was unhappy I didn't keep a log of every day I drove. I told him I was mostly local, and the law only requires me to use a log book outside of 100 air miles from where I was dispatched. Unhappy with that answer, he told me to call my employer because he wanted to talk with him. It was late and I told him the shop was closed, but I'll try to reach him at home.
While I was trying to call my boss, the same clown went back to my trailer and started to give me orders for a safety check. I wasn't paying attention, and his idiot buddy came running at me screaming his brains out. I told him I was only doing what his coworker told me to do. His face of anger fell, and he said "oh, okay."
When I got home, I emailed a letter to my state rep. I also copied it and sent the letter to the Governors office. I lied a bit and told them I had video of the entire event, and I was about to put it on Youtube to show people how our public servants treat their citizens. I only heard back from the State rep promising he would look into the matter, but that was the last of it.
A month later I had to go to that company once again, and once again had to go through that same weigh station. Both idiots were gone, and they had new officers at that weigh station.
That's how you handle things.