If you are worried because you no longer "feel pregnant," you're certainly not alone, and there's almost no need to be concerned. Most likely, you are simply feeling the rapid stabilization of hormones that occurs after the placenta develops and the journey into trimester-two begins.
During the first trimester, you will likely feel more pregnant than at any other stage, because your hormones are very rapidly adjusting to the new life growing inside your womb. Levels of estrogen, progesterone and the pregnancy hormone HCG increase rapidly, and you may feel all the characteristic signs of pregnancy-- aching breasts, cramping, nausea, vomiting, extreme fatigue and emotional swings.
After the twelfth week, your hormones have stabilized quite a bit more. Your baby's vital organs and body are formed, but still need many more weeks to grow and develop. The re-orientation toward growth instead of creation will cause you to feel far fewer signs of pregnancy. Because it's likely that you haven't felt the baby's movement yet, you may not feel pregnant at all. As a result, you may fear that you are not pregnant anymore, or that your unborn baby is in danger.
Unless you are showing other signs of impending miscarriage, such as bleeding or abdominal cramping, your baby is almost certainly safe. Remember that, by the time you enter the second trimester, your risk of miscarriage has declined significantly.
Nevertheless, there's no harm in following your gut instinct. If nothing else, a quick visit to your doctor or midwife can demonstrate that your baby is safe and sound. Talk to your practitioner if you don't feel pregnant anymore any want to be reassured of your baby's safety.