So what's the difference between 'sentir' and 'sentirse'?
I'd always assumed it was something to do with one being more subjective (I feel ill) as opposed to physical (it feels hard).
Well (surprise, surprise) I was wrong.
In meaning, at any rate, they are the same.
What differs is the structure.
As simple as I can make it . .
Siento = I feel - followed by a noun - e.g. annoyance, happiness
Me siento = I feel - followed by an adjective - e.g. annoyed, happy.
That's all there is to it!
To remember which one to use a noun with, I think of the phrase for 'sorry' (lo siento) which literally means 'I feel it'.
'Lo' is a pronoun (stands in for a noun) so, as long as you remember it's 'lo siento' and not 'me lo siento', you've just mastered another part of the Spanish language ;¬)
Of course, I can't let a discussion about feeling pass, without, at least, mentioning 'estar', 'dar' and 'tener'
Phrases using 'dar' and 'tener' are like the ones using 'sentir', in that they use a noun.
So, three ways to say 'I'm hungry', using the noun 'hunger'
Siento hambre (I feel hunger)
Me da hambre (It gives me hunger [makes me hungry])
Tengo hambre (I have hunger) - This is the phrase you will normally hear - the others are just for examples of structure
Or, using the adjective, you could say (although you probably wouldn't)
Me siento hambriento (I feel hungry)
Estoy hambriento (I feel hungry)
There are some phrases which are more commonly used 'set' expressions, like 'tengo hambre', 'tengo calor' (I'm hot) 'Estoy caliente' also means 'I'm hot' but, if you're a woman, I wouldn't recommend saying it to a red-blooded latino, unless you're prepared for the results ;¬)
There's also 'me da pena' (it pains me) and you'll no doubt come across several more, but now at least you can begin working on your own set of alternative expressions.
I hope you're not feeling too confused after all that ;¬)