Complaining vs Not

Today, I am confused.

Lately I've been in some degree of pain.  Let's focus on the physical for a moment, though I think this discussion spans the gamut (physical, emotional, mental, etc) of pain.  Last weekend I got sunburned.  It's certainly not the worst sunburn I've ever had, or that ever has been, but it still hurt pretty bad.  It still does, in fact.
Now, I'm a fairly friendly and even-tempered person once you get past my introvert nature, but the last few days I've been increasingly surly, whining to myself about all the ways it hurts.  Not being the type to impinge on other people, I keep it to myself.  But finally I just couldn't stand it any more, so I wrote about it on a private forum.   On the one hand, it was a relief to finally get it out there but on the other I was overshadowed by the feeling of 'what if someone I know reads it and it hurts them?'  Worse, in the end, it just made me more surly and irritable.  Spreading and nurturing negativity does that, even if it's just within yourself.
In my grouchiness this morning, some bright chipper sunspot posted on facebook something challenging the hapless passerby-er to "go 24 hours without complaining and see how your life starts to change!"   I growled at it and scrolled past, especially since that is my usual modus-operandi which I was currently and deliberately eschewing.  
But darn my brain!  It won't let it go.
So now I'm stuck trying to figure this out.  Sure, let's go 24 hours without complaining, I like to be happy.  But I don't like ignoring the pain.  That never turns out well and tends to make an injury heal slower, incorrectly or not at all, tearing the wound open further.
So where is the difference?  At what point does my expression of the pain to someone who might help become a complaint?  Can I be positive while still being honest?  No, I can't say 'it doesn't hurt, don't worry about it' - that is a lie.   How can I make you see the depth and serious nature of the injury, that though it appears superficial to you it's real and painful and valid to me?  How does one do this without crossing the line of being a whinny complaining (insert appropriate noun of your choice)?
The problem with complaining is it breeds negativity and ill feeling.  How often, perhaps, do Drs go in to see their patient and ask "How are you doing" and the patient replies "I'm doing well!" when they're obviously not.  I wonder how often the Dr thinks "If you're so great why are you here?"  We're so obsessed with not letting people see our pain, we can't complain!  But this just leads to holding it in and the injury festers. 
But constant complaining isn't any better.  No one wants to be around a pessimist, the ones who are always bringing you down, who can never say a positive thing.  The ones who are made of complaints.  They exude as much negativity and bad feeling as holding in your pain.

So, again, the question how can you tell someone it hurts and it's a problem (and have them really understand) and yet still not complain?  There must be a balance somewhere, but where? and how?