Yes and yes.

You loose a degree of peripheral vision in enclosing helmets - though be aware that modern reproductions sit further away from your eyes than they should and are a lot more restrictive in this than they used to be. Taking advantage of this was very common, there are medieval manuals where a guy in melee combat with an opponent intentionally closes his visor to deny him that sight (and also examples where he opens it to stab him in the face).

As for hearing, the biggest culprit is the padded cap under your helmet - once you tie it properly under your chin, your hearing gets way worse. If you put a helmet on top of that, you need to raise your voice to even talk with the guy next to you. This is a feature, as the noise of an axe slamming into your helmet is... less than silent. It's even possible to not hear your commander yelling at the top of his lungs from 20 meters away when you're in the middle of a shield wall that's being engaged.

Taking advantage of the latter is a big part of medieval warfare - once a formation engages, only the most elite of units will be able to disengage in good order, if at all, and they are feared for that accordingly. Usually, someone routs. As for example, Battle of Rozhanovce saw Hospitallers turn their entire unit 90 degrees in the middle of a major battle to reinforce main body of their army, which is mentioned as a big achievement in the (written some 30 years later) Chronica Picta.