I have synesthesia, and for me, it shows up as temperatures and sensations in my head relating to sound. Lower sounds tend to feel warmer, and higher sounds tend to feel cooler. I physically feel like my brain is being touched by sound.
I thought everybody felt these feelings until a few years ago, when my friends informed me that, no, it's called synesthesia, and not everybody has it.
Other odd synesthesia things for me is that sometimes white tastes like those butter mints you get at weddings, and sometimes yellow tastes a bit like lemonade. When I was 3-5 years old, violet-red and red-violet crayons inexplicably made me nauseous. I had to figure out how to overcome that nausea, but I don't exactly remember how I did it. I just remember it sort of felt like overcoming a fear.
I do experience that ASMR thing, but I don't know if it's because of the synesthesia or if it's a separate condition.