My directional pad isn't physically responding like it should, as if it is sticky. Why is this and what can I do?

Chris, It is likely that the device battery simply is dead. In this case, charging the device should take care of the issue. If charging doesn't work, I will refer you to the Nintendo Wii U Pro Controller Troubleshooting page to help you better identify the issue: Nintendo Wii U Pro Controller Troubleshooting