Hi hun! DONT STRESS..it is completely normal to feel like something bad could happen to your unborn, especially when carrying two! I've never had twins but I have been pregnant before this time around and I could go on for days telling you what I was afraid to happen to my unborn!! It is completely normal. Not to mention, many women carrying twins go into labor a month or two early so even if anything were to happen to make you go into early labor, they'll be okay! relax :)
It is normal. I was afraid until my daughter was like 8 months old. I really worried about her smothering or SIDS. I think it's first time mom jitters. I really hope this helps to calm you. The babies will be fine. When ur stressed, just pray. God has the final say!