Oh PJ only you can decide that. It's why dejags left after all. But she left the internet in general as she found google to be just as bad, if not worse.
What you have to decide is whether or not you are able to change the way you read things. MN is an absolute wealth of knowledge/help/amusement/support if you are able to read and use it in a healthy way. Firstly, and I love you remember, even if you read 7,000 tales of 'it's just a cold' and just 1 of 'it was a terrible, incurable mutant bug', what your anxious mind attunes to is that one possibility that it might be more serious. Well, frankly, that's life. There are risks in every situation, there will always be the one who is the exception to the rule. When you drive a car, accept a drink in a bar, cross the road and turn on the gas cooker, you do so knowing there is a minuscule chance that something could go horribly wrong. But you don't panic because you know that it probably won't. You need to be able to parent in the same way. You need to do that for yourself and for Lexie. Chances are she will sail through this life with fabulous experiences, wonderful friends and a great family. She will also fall down, be ill, not get the job she wants, have her heart broken, God forbid, she may have unruly hair. You will be there to support her through that as and when it happens. What you cannot do is imagine things that aren't happening or worry about them because precious moments are slipping by and you're not enjoying them.
Say you leave MN and you're sitting in a cafe with a snuffly Lexie and you overhear the woman on the next table talking about mutant super bugs that manifest as a snuffly nose. Is that not the same? Will you resist the temptation to google and read all the highly improbable stories of evils around every corner? What's ideal is that you use MN to inform and convince you that things are alright. You talk to us, you ask for other opinions, you take heart from the tales of how others get through a neverending virus.
The other thing is, the nature of talk boards. Example: if you post a thread saying 'my dd had an injection 3 days ago and her arm is swollen still', several things will happen. Most MNers, all of whom have probably seen their child injected at some time will not click on your thread or leave a comment because they will shrug and dismiss it. Luckily, they know a swollen arm is usual after an injection and can last for weeks. A few, kind, selfless MNers will click anyway and reassure you. A couple will scream PFB and laugh about it. What will certainly happen is that those few MNers whose child/friend/neighbour's 3rd cousin's dog had a bad reaction to an injection will come and tell you their story. That is because your thread title piqued their interest, it reminded them of a tale, they have a vested interest. Now, what you should be able to do is read the lovely reassurance, stick 2 fingers up at the teasing twits and bear in mind that yes there are tales of it all going wrong and here are some examples, but you knew that there is a risk involved anyway. These tales do not alter this fact. And you know what, MN can actually help in these situations. Somebody might say, I tried this with my dc and it worked. You may never have thought of that and it may work for you too. That's why we post, that's why we keep coming back, because it might help. If you're coming back to feed your anxieties, if you know you're not going to be able to resist reading the horror stories and being affected by them, then perhaps we must lose you on here for a time.
I don't have the answers (but I have a lot to say apparently), but I know that you and Lexie deserve you being able to find a way to deal with anxiety. I don't know how. Heck, I do it too. Sometimes pretending I know what I'm doing helps. Oh look at me, I'm coping, administering medicine, soothing my child, not panicking and once I've pretended for a while, you know what, actually her temp has come down and she's fallen asleep. You need to find a way of getting through those horrible bits and not letting them affect the lovely bits.
And, er...
Please don't leave. I'd miss you.