'Nirvana' - really an experience of enlightenment or 'realisation' is more than just pleasant feelings. In Buddhism we count a direct experience of something called 'Emptiness' (that doesn't mean non-existence) as the first step into it.

A higher state again is called 'cosmic consciousness' by some traditions. If you do a Wiki' on both terms, that'll help. In both states you experience yourself as being all of reality, not from your own POV, but as reality itself.

Don't think of it as a place or somewhere spiritually different from right where you are now. Nirvana/Enlightenment is the realisation of your true nature, how you really exist. Usually after either experience you find that your desires and needs have all but disappeared, thus leading to happiness and feelings of well-being.

MelT