There's nothing called heaven or hell.. Its all wat we do, if we take good decision we do good work which give pleasure to our mind its heaven.. But if we take bad decisions nd do harm to others it shows us hell..
Mind shows us heaven or hell based on our work and whatever mind does is imaginary so both are imaginary.. After every bad things or harmful activities our intelligence becomes weaker nd mind will diverses, this diverse state of mind makes us experience hell..
A stronger intelligence which comes after we do good understanding, which will tell our mind there nothing hell or heaven,ultimately relaxing it..
So wat should be done to get rid of bad feelings.. Start doing something which wl give happiness to ur heart (asa kam kro jisse andar se khushi mile). Dis happiness will help in getting rid of bad feeling, nightmares nd especially ur imaginary hell..