When you feel overwhelmed, your brain is telling you things are "too much." But what if your brain is tricking you? With ADHD, that can easily happen if you try to process information or learn in a modality that you're not strong in.
Modalities for learning and taking in information are the senses of visual (seeing), auditory (hearing) and kinesthetic (touching or movement). When you learn best with visual information, but you're expected to learn and remember just by listening alone, your brain will struggle. If hearing is a weak modality for you, your brain could feel overwhelmed and shut down. There may not really be too much information for you to process, but unless you can see it, it would feel that way.
Find out how the way you process information best affects how well you learn, remember and respond. Using your strongest modality or the right combination of modalities could greatly reduce your sense of overwhelm.