Hola Beki, 

You’ve put your finger on the issue; knowing the noun and adjective forms is the key to choosing the right form of sentir, and this is summarised so well in the yellow box TIP in the lesson.

The language of feelings, and emotions is something that practically everyone struggles with; ask any therapist. Some time ago I went through the dictionary [WordReference is a great online Spanish-English choice] and wrote out the noun and adjective forms of every feeling / emotion that I could think of in Spanish and English. It helped a lot, not least because I got a lot of surprises. Since doing this, I do a mental check of what is the noun form, and what is the adjectival form, and that points me to sentir or sentirse. The teachers work on the basis that a noun is a thing, so it is WHAT we feel, and an adjective is something more descriptive, so it is HOW we feel. These are the rules we have to follow in Spanish.

It all goes pear shaped when we translate into English because of modern usage, and overlaps in translation of nouns and adjectives, but it is a good discipline to think of nouns as “whats” and adjectives as “hows.” Saludos. John