There is an extremely loud, violant knock that apeared from thin air Please help

Roughly 575 miles ago i had my head gasket replaced as well as a valve job. I was told to take it easy for the first 500, which i did. Today was the first day i drove above 65mph, i hit 80 /85, no problem. A few hours later i got back on the freeway doing 80ish and when i exited there was a intense shutter, i thought it was going to stall the whole way home which is only a few blocks. Along with the shuttering there was the loudest engine knock i've ever heard. I looked under the hood and under the carriage, aside from the block which was vibrating loudly I saw nothing. no leaks no loose hoses nothing. I'm not sure if the engine was moving more than it usually does well i would say 90% sure. Keep in mind I was trippin. But the sound is unmistakeable, I want to know if theres anyway that the mechanic may have made a mistake or is it just my unbelievably unlucky misfortune