The trauma of labour is hard enough. Seeing someone you love go through such a painful process (some people say it's wonderful...good luck to them) is traumatic enough, but the stress and strain of bringing home your first born is beyond that. It needs it's own word as traumatic doesn't seem to do it justice.
Doubts and fears will cross your mind, doubts and fears that were not there during the pregnancy. What seemed like it would be the simplest task, feeding (they make all kinds of noises when bottle feeding so don't worry), or changing a nappy becomes the most stressful Mission Impossible, particularly when your baby is crying.
Whilst we're on the subject - the crying: don't be surprised when it gives you a feeling in your stomach like nothing you've ever experienced. Terror, panic, stress...they all happen and then you feel an overwhelming need to soothe this and it can break your heart but it will stop and you will have helped it stop so feel good about this.
From a mental standpoint I can only speak from my experience. What I feel now, 7 days in, is so much more complete than I have ever felt before. You may feel detached those first few days, particularly as you WILL be sleep deprived because you want to check on your little one constantly, but after the first week it will all start to make perfect sense. You and your partner have created something that is made from love and will be loved by you both like nothing else on earth. Enjoy every moment, but don't feel bad if it takes more than a few days to get there. (One last things - remember your partner..show them as much love as you did before..they need it too).