Adrenaline is a hormone secreted when we are in danger, when we feel fear or anxiety. It blocks the secretion of endorphines. It sharpens all your senses and makes all your perceptions more intense. It is the last thing you wish for while in labour.
Elliminating fear and anxiety is essential. If you anticipate pain and you are afraid of it, this is very likely that you will indeed feel it. If your previous birth was painful and you do not believe it could be otherwise, you might consider hypnobirthing, which helps you to forget about fear. Hypnobirthing training can help a woman get into the birthing trance if she cannot reach it naturally, having lost confidence in her body.
It is important to avoid whatever triggers adrenaline secretion: sharp lights, noises, stress. Adrenaline secretion is contagious - if someone in the same room is being nervous, this will interfere with your labour hormones. A husband who is deadly scared, even if he manages to hide this feeling, can actually slow your labour down.