Do you have chronic jaw muscle pain?
You could be clenching during the day.
A study shows that people suffering from chronic jaw muscle pain clench their jaws more often during the day than those who do not. Even if you do not have chronic jaw pain, you might notice occasional jaw muscle pain when you're focused – working, driving, or gaming.
So whether you have chronic jaw muscle pain or not, daytime clenching is real and can affect you whether you're aware of your clenching or not.
Cioffi et al., “Frequency of Daytime Tooth Clenching Episodes in Individuals Affected by Masticatory Muscle Pain and Pain-Free Controls during Standardized Ability Tasks.” Link to study