Nothing serious I hope. Wishing you a speedy recovery.
The D300 was a great little camera in its day and judging by the quality of your images taken with it, it still stands up well today. My first really good DSLR was a D200, the one everyone seems to be clamouring for these days because it had a CCD sensor and the alleged CCD look is in vogue at the moment. But as I remember it, when I replaced it with a D300 it brought a massive step up in image quality from its predecessor.
I gave it to my dad when I replaced it with a D7000 (not quite the upgrade I'd hoped for at the time), but I recently reclaimed it after he passed away. I'm not really sure what to do with it these days, I should probably see if the battery still holds a charge and take it out for a spin.