I feel this. I've found there are a number of possible causes. The most common one with the biggest impact is not getting enough quality sleep, as sleep quality

I feel this. I've found there are a number of possible causes. The most common one with the biggest impact is not getting enough quality sleep, as sleep quality often declines as you age and under stress (life is most stressful in your 30s and 40s). Restrict your caffeine intake and improve sleep hygiene, it makes a big difference, as poor sleep affects short and long-term memory, cognitive speed and mistakes.