Everyone probably goes through what you're going through a little bit. I still check on my kids at night and they are 4, 6, and 8 years old. You probably need to seeing a doctor for your anxiety. Your hormones are going through major changes right now and that is probably a factor in your fear.

I did a little Googling and found an email support group for siblings of SIDS babies. It might help to talk to someone else who has been what you've been through. This is a harder time in being a parent with everyone being so new. It gets a little easier. Take care.

Here is a link that might be useful: SIDS Families Support Groups

I think all parents worry about this. I did in the beginning a lot too. I think my husband was more relaxed about it and eventually I relaxed more too. Just educate yourself and remind yourself of what "not" to do... that's the best you can do. You cannot watch your baby sleeping every minute. Plus, if you are are exhausted you are more likely to make a mistake of any kind. We just put our baby to sleep like they did in the hospital. Try calling a nursing info line and they can suggest specifics for you.

First of all, I can't imagine how much more fear I'd have about SIDS if I'd had a sibling die of it and had seen the impact on my family. Try to keep things in perspective though (I know...easy for me to say!). You mentioned the most important things - you don't drink, don't smoke, and most importantly, you don't lay your baby on her tummy to sleep. The rate of SIDS has gone down tremendously since the recommendation became that we should lay our babies on their backs to sleep. They just didn't know that back when your baby brother died.

Have you thought about getting a bedside sleeper (like the one made by Arm's Reach)? This type of arrangement might give you a lot of comfort without the risks associated with having the baby in the bed with you.

Also, I'm glad to hear that you feel "normal" during the day, but do you think it is possible that you might have a touch of post partum depression? PPD also tends to increase anxiety. I think talking with your doctor would be a good idea.

I hope that you find ways to feel more relaxed and get some sleep soon. I know that whenever I am feeling anxious about anything, it feels 10x worse if I haven't been sleeping well!!!

When I read your post, I just had to respond. Although this has nothing to do with pregnancy, I distinctly remember that, prior to getting my period, I would often have these overwhelming feelings of imminent doom. They were horrible. Since you are at a point where your hormones are trying to get back to a normal level, this could have a great bearing.
When I first brought my new baby home (many years ago) I also recall mentioning to my doctor my concern about SIDS. His response was that babies (or anyone) instinctively respond to avoid this situation.
Just think about what you would do if you awoke to find yourself face down in your pillow. You'd move your head, turn over, or do whatever it takes to get out of this situation.
I kept our baby in a bassinet next to my bed for the first few months. As I was always a very sound sleeper, my greatest fear was that I would not wake up. However, I soon discovered that new mothers suddenly acquire "mother's ear" and wake up instantly at the slightest stir of their little one.
The fact that you acknowledge your fears is a good step toward overcoming them.
However, it would still be wise to mention this to your physician, for it sounds like your hormones are wreaking havoc with you.
I wish you well and hope you are feeling better soon.