Can you have a boner during flatline?

Hi all.

Been on nofap for 15 days. Over the last 2 or 3 days I have had a huge reduction in libido. I feel less interested in women; i was already not feeling interested when i went through ED while trying to have sex with my gf a few weeks ago. Porn seemed better than sex. But now my interest in women has become even lower. Amazingly, i dont even feel like fapping. From being horny 24*7 to not wanting to fap at all seems surreal and a little saddeningly scary.
However, today while I was on my way home, i saw a thinly clad hot lady on the street and immediately got a massive boner. Is it normal to have a boner during the flatline? Or have i not entered the flatline yet.