A DM should never ever tell a player how their character feels. You can try to evoke emotion through your descriptions of the world, but you should never say “you feel scared”. Because the player is going to immediately say, or a least think “The hell I do!” Players need to feel like they have control over their characters. And there’s nothing more intimate about a character than what they think and feel. Unless there is some magical compulsion affecting their emotions, you should only describe what the characters experience with their senses, and let the player decide how their character reacts. And even magical compulsion should be avoided in all but the rarest of occasions, because players hate it. Most players would prefer their character be knocked out than forced to run away in fear.