I went through it the first few months of my pregnancy. Up till I was 13 weeks and had a scan to see if there was any growth I had myself convinced I had had a missed miscarriage. I would still get symptoms, I just didn't feel pregnant and nothing could convince me otherwise. I just gave birth 5 days ago to my baby girl, and she's perfectly healthy. It's normal to worry. Just try to enjoy your pregnancy. If the worst does happen, it is better to reflect on being happy about it rather than look back and only have memories and fear and stress.
I didn't have any symptoms other then sore breasts until about 6 weeks and then the nausea and fatigue hit hard! I have a coworker who never had MS/nausea and her little boy was born happy and healthy about a month ago. Try to relax and enjoy the time without symptoms cause once they hit it can be awful. I'm 11 weeks now and have barely been able to get anything done around my house for the past 5 weeks, I drag myself to work every night, and eating feels like a full time job in itself! Most likely everything is just fine and chances are as your HCG levels continue to rise you'll start noticing more symptoms.
It's normal to go through such a phase, I was pretty worried myself, often wondering if I was really expecting, I had a symptomless first trimester, and a very radiant 2nd trimester. Now in my 32 week, it seems everything has hit me all at once. I would suggest to try to take it easy though cos worrying isn't good for your baby, and neither is it good for you.
The comments in your pregnancy book is just so that you are aware of the probability of it happening. If you are taking your vitamins, and are receiving health advice, you should be fine. All the best..xxx :)