TMI weird topic (no pic)

Ok...so my SO and I have been together for 2 years, and have sex around 2 or 3 times a day, 4 or 5 days a week. He usually can last about 30-45 min, sometimes longer.

But yesterday, even though there was nothing different that we tried, he couldn't last longer than 5 min. and the only way he could describe it was that I felt different, in a good way.

What could have caused that?