I've had some flu / viral thing where I've been struggling for breath for weeks. I ran every day in September and October then haven't managed a mile since then. I went to the doctor, who more or less said only time will help and usually it's around six weeks for one of these things to clear. I've even been struggling to run upstairs to get my coat or go to the toilet. I usually say (only half joking) that my usual fitness test is if I can run up our stairs then I'm okay (if I can run upstairs, then I can probably run a mile, and if I'm okay for a mile then I'll probably be okay for a leg of a Bob Graham...etc)
This morning I've just managed to run up and down stairs five times. I've never had my VO2 measured but my mate John, who does triathalons, said to me that my 'aerobic base' should be good, whatever that means. I'm hoping I might just be on the comeback trail at last. I certainly hope so because being out of breath has been quite alarming at times and as usual when I've not been running I've put on weight, which needs to go and soon!