I just got the garmin forerunner 10. I was using the 305 for years but it was just way too big & was getting awful at locking onto the satellite. The 10 I love already, only thing it doesn't show pace on same screen (you have to press a button) but I've not found this a problem & I've set the virtual partner. It's on offer on Amazon for about ??50 at the moment which is good value.
I've had a history of thyroid problems (under-active) but I had glandular fever a few years ago and my white blood count is low so I get more viruses now when I am training more (higher mileage etc). I don't get colds a great deal but I get swollen glands and an anaemic type of fatigue (even when my iron levels are ok). So have to be careful. Eating well/resting is important when the body is giving these signs- I've learnt the hard way and ended up ill/injured by not listening!