Going long

I hadn't run a long run since atleast a month.And all of my longruns so far haven't gone beyond 16 kms. So I decided all of a sudden yesterday, that I am going to do 20kms, no matter what. The 'no matter what' was responsible for my not so good experience during the run...

My normal long run of 16km is twice the road race(held every april) route. The road race route passes through some prominent landmarks in iit campus like football, hockey fields; computer centre(cc), Hospital, Vanavani, Gate, Gc and ends in the stadium. So for yesterday's run, I added another 10 laps in the stadium to make it a 20km run.
I usually carry two 250 ml bottles(the ones you get to flick on an IA flight) during the long run. This time I decided to mix some glucose in the water...which didn't turn out too good.
I started off well at around 9 min/mile pace and was comfortable until I completed 8kms(i.e. when I reached the stadium). From this point I was struggling, with my left calf really tight, for atleast another 10 mins, after which I felt a bit strong again till the 16km mark(stadium again).
My pace during the run so far had varied from 8min/mile to 12 min/mile depending on how I felt. But as I started off the remaining 10 laps of my run, I felt very weak and tired. I was just pushing myself, counting the number of laps remaining, trying to shake off the fatigue. My head started wobbling and my form had degraded, I was more shuffling than jogging. Since I was sipping glucose water rather than water, I felt a desire to drink pure water..I even imagined the coolness of water rushing from a spring somewhere in the hills...The thirst was becoming unbearable and I had to finish the run quick.
Somewhere around the 7th lap, I thought how could people be insane enoguh to run a marathon, when here, I am struggling to complete a 20 km run. I sort of decided that I wouldn't attempt a marathon or distances beyond the marathon, atleast not in the near future. Soon, there were only two laps remaining and I slowly picked up the pace and the last lap was run really fast..I just wanted to get it done. I was really relieved that I had accomplished the goal I had set for yesterday. It had taken me 1hr 59 mins to do it. The day before yesterday, I had done some speed workout and that might have made yesterday's run, a tad more miserable. After finishing the run and having cooled down, I headed to the hostel and I drank 1.5 litres of water straight, had my grub and slept soundly for a good 10 hrs.