Why does my newborn startle so easily?

Yup, like what was mentioned, your baby is exhibiting Moro Reflex. It typically happens when baby’s head changes position abruptly, when he/she hears a loud noise, or when baby experienced a sensation of falling (e.g., when being lowered into the bassinet with a lack of support). There’s no need to worry about this and it will decrease with time. You can try providing extra support when transferring him/her from one place to another to minimize the occurrences. If your baby frequently startles himself/herself awake, you can try swaddling to see if it helps. :)