Weird symptom?

Sooo this caught me off guard, I'm guessing it's maybe more common than I thought but, after a week of iron supplements, I've suddenly realized I'm able to be startled again. It's almost as if I lost the ability to even have my nervous system react appropriately to external stimuli? I'm not even sure how to describe it, it was just crazy to think that I can't recall the last time I was startled by something behind me and actually had my body respond appropriately and with a normal reaction time. I'm hoping this is a good thing? Anyone else have this happen as their mind/body was slowly coming back online?