Brain hyperactivity can make things seriously difficult for you. Even just productively making it through your day can sometimes be a challenge for a number of reasons. Your mind might race, it can be difficult to focus, you may be an A-plus procrastinator, or deal with certain mood disorders — the signs you have a hyperactive brain are varied and can affect you in many different ways. If you're dealing with a hyperactive brain, that doesn't necessarily mean that you have an adult form of ADHD or any other condition, necessarily, but some of the signs of a hyperactive brain can also be signs of diagnosable conditions and if you have any concerns about these sorts of signs or symptoms, you can certainly bring them up with your doctor so that they can hopefully determine if there's something that needs to be treated or not.
Even if there are signs that you have a hyperactive brain and you don't have any sort of condition — which is never a given — it might help you to better understand what you're dealing with and also, if needed, figure out what sorts of things you might be able to do to help you manage the signs or symptoms. If you suspect that you might have a hyperactive brain, keep an eye out for some general signs.