I'm 23 weeks and my baby has days where she's not as active. You have to remember that they still sleep a lot and still small enough to turn and you may not feel kicks due to the position. But if you ever feel like something isn't right don't hesitate to go and get checked out.
Dont worry it will become more of a reality around 30 weeks. You'll feel your baby more and this will help you grow more attached to he or she. Good luck, I was exactly the same way and sometimes I still feel detached but I assure you its normal. When the baby arrives there will be a whole new feeling of appreciation and accomplishment!
Don't be sad there will be times when the baby isn't as active as other days but it just means that they are growing and have less space to move around in so all they do is sleep if it really worry a you drink cold water put music on so he/she can hear (: