system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do I sometimes sweat more when I'm nervous than I do when I exercise?  

I am a physically fit male and I drink a lot of water. And yet even during intense workouts I seem to sweat a lot less than when I get nervous. More specifically, when I am forced to speak in front of an audience of some kind.
gpt
When you work out you sweat because your body is heating up, and one way to remove heat from the body is through evaporation of sweat from the surface of our skin.  
Now when you are nervous your body shifts into into a "mode" that we call "Fight or Flight." In this mode several things happen: chemicals are released into the body that cause us to get ready for fighting or getting away (hence fight or flight). These chemicals cause blood vessels near the skin to get wider and vessels near your intestines and kidneys to get narrower. This causes more blood to go closer to the skin where heat can be transferred to the surface to the skin and then away from the body (so you don't get too hot), this is why you get a bit flushed as well. 
These chemicals also cause your heart to speed up, your breathing to speed up, making your eyes dilate, and make you anxious and want to move around. Sweating is also part of this response, it helps the body in the same way as before but in this case it is a preemptive measure. 

Many things trigger this fight of flight response: heights, large animals, something that scares you, or anything that makes your nervous.