Heaven, increases all feelings to their extreme quality. Hell, decreases all feelings to their minimum quality. So if someone dies feeling sorrow, rage, hate and goes to heaven they’re going to feel all those to their extreme, that is why god creating hell is actually an act of love because he wants us to feel sorrow, hate, rage as little as possible and feel love to its extreme.
I can’t say for sure what religion you’re talking about, so I don’t know much of the religious context for this definition of heaven and hell. My issue with this definition is emotions are so much more complex than “happy is good, sad is bad”. A lot of people who have dealt with depression (including myself) will tell you that it’s far worse to feel nothing at all. I’d much rather feel the sorrow or hate, and have help from God to work through those feelings.
I find the Christian (specifically protestant Arminian, and yes that is my religion) answer to this question much better. Basically, hell is the other option to heaven. Heaven is where God is fully present, so there must be somewhere else for those who reject God to go. That place must be fully apart from God, otherwise he would not be honoring their decision, and so he would not be all loving.