Parathedox

Sometimes, in a battle, if I've got the slower Pokemon and I try to use a healing item, the item will not be used unless I take damage, and if I try using it again the next turn, or if the battle ends in any way or my Pokemon faints, the first use will not have any effect at all. As an example, I was fighting a paralyzed Pidgeotto with my confused Roselia (I think?), and I tried using a Super Potion, since the Roselia was low. The Pidgeotto couldn't attack, and my Super didn't go through. I used Mega Drain on the next turn, and the Super went off only then. As another example, in a similar situation, the opposing Pokemon either didn't use an offensive move or didn't hit me for some reason when I tried healing, so the healing didn't go off. In the next turn, I tried healing again, then it went off, but I had already used two Supers, and I think I only got the effect of one. If there's any insight that can be offered, it would be very much appreciated, even if I'm just missing some mechanic I'm not aware of. Thanks in advance.