Who hasn't felt it? The pressure? The overbearing presence of the silent room as you sit there staring at a computer screen or paper, just trying to get your brain to function. It's panic. Fear. Terror. And it's one of the worst feelings. Afterward comes the blame. Knowing the information and losing it in that moment.
I know that feeling, but there are tons of techniques out there to help you. Lots of different little things. Like breathing deeply. Not everything is going to work for everyone, but let me go through two of my favorite.
Scent cues. It may seem silly but a lot of memory is tied to scent. So, wear the same perfume or cologne when you study as when you go for the test and save it just for class. Then when you start to panic, sniff your wrist. See if tying the memory to scent helps you remember, the physical action of sniffing can help break the tension too, not everyone works that way, but it's worth a try.
Alright. On to my favorite! Visualization. Similar to the scene in Harry Potter when they faced down a Bogart, turn the test into something silly. Use your imagination and make that bear trying to eat you sit on a unicycle with a party hat.
Again. Not everything works for everyone, so don't be afraid to try different things. This is why we have so many different methods out there. To accommodate a thousand or more different learning styles. Don't beat yourself up, what works for someone else may not work for you.