Running on empty

Well interesting day so far, I went out today for my usual lunchtime'ish 6 mile run and had a torrid time of it. I started off normally but by the time I had done the first mile and a half I could feel things weren't right. I felt tight and my breathing wasn't settling into its usual rhythm, thinking it was just taking me a bit longer to settle down I carried on, but as I got further on my legs were getting heavier and heavier. With this going on I decided to revise the distance and cut it short by making it an easier 4.5 mile route. However my energy was just depleting with every step so I ended up walking in sections just to give myself some respite. It wasn't that I was completely put of breath or anything like that, my body just wasn't giving me what I needed to keep a steady pace. It has been a long time since I have felt that sapped on a run and considering I have been running through torrential downpours and freezing winds ironic that on a mild ish day I conk out. Sitting here now thinking about what could have caused this I believe a combo of a pretty heavy, starchy diet the last few days with a lack of sleep (only been getting about 5-6 hours for the past week) has just drained me. I need to try and get a bit more fruit and veg into me and hopefully catch up on my sleep for the next few days as this weekend I have set myself a goal of an 8 mile, slow, run to see what a real distance starts to feel like. I just need to bear in mind what my body has told me today and do something about it.