There are different attitudes,congestion and interactions for cyclists in different cities. NYC drivers seems particularly antagonistic towards cyclists, I have seen many examples of what seemed like intentional strikes to me by taxis and commercial drivers who are likely to be more time crunched and build up a frustration towards cyclists. But cyclists also seem to be of a more daring rugged stock there too.
Granted, my only personal comparison would be to Buffalo, Albany, Poughkeepsie and San Diego, all which have much less congested city centers.
The only east coast city that matched the "needles and feces" attitudes I have seen was Philadelphia. As soon as you start driving into the city it is impossible to notice how much trash and car debris is in the road. The moment I parked, we saw needles on the ground and as a result I was more likely to notice I imagine. But, it was truly a filthy city.
Buffalo city centers do have a high rate of panhandling and street scams, you just learn coping skills.
Until the pandemic I commuted through London by bike for about 7 years - ranging from 5 to 12 miles a day. I fell off maybe a couple of times, never hitting my head. If the OP is sustaining multiple concussions from bike riding, they're either riding a lot (bike messenger?) or riding very recklessly (or perhaps both).
