To an extent, it depends on the subject being learned, but feelings do have a large impact on learning in general. If you are not feeling well emotionally, it is very difficult to focus on whatever you're trying to learn, sometimes even if what you're trying to learn about is of great interest or very important to you. Emotions are extremely distracting. One of the worst ways emotions affect learning is if the subject you're trying to learn about is the CAUSE of your negative emotions. For instance, if you're studying... Let's say chemistry. You're in college, you've got your major firmly set in your mind, and chemistry is one class you must pass to graduate... And you're failing. But it's only midterm, so you might be able to save your grade by the end of the semester, yet when you study it feels like the more effort you put into it, the less you retain. Because you've put so much pressure on yourself to pass this class that your anxiety levels are too high to learn as much as you need to- your anxiety won't allow you to give the material your full focus. That's just one example though. Other emotions can have a big impact too; depression makes focusing extremely difficult because it's so hard to 1) make yourself believe that you're capable of succeeding, and 2) make yourself care enough about it to be focused. Positive emotions can affect learning just as much though. When you feel positive and content, you're most likely going to do well at whatever you're learning. If you're especially happy for a particular reason, it may slightly hinder your learning because whatever you're so happy about is probably going to be your true focus and be a little bit distracting.
