Bonking the long run

Today, I bonked. I failed. I was taken out of commission by the naysayer that lives within my head.

I was on tap to do a 14 mile long run this morning. Normally, even though I am incredibly slow, I don't mind long runs. In fact, I kind of like them! I get into a groove, I get into a mindset, and I just keep going. Today, I just couldn't keep going. I knew within the first mile that this run was going to be tough, and it was all downhill from there. I kept having these very negative thoughts about running and my ability to run. I couldn't shake them. This negativity seemed to be battering me from all sides. I just kept circling variations on the following: I'm too slow. This is too long. My feet are going to go numb at any moment. My calves are going to cramp. Why is it so warm? What kind of runner are you. I can't do this.

My 14 mile run turned into a 6.5 mile walk. A brisk walk, but a walk nonetheless

I was defeated not my my body, which was not crampy or numb or dehydrated or underfueled. By all rights, this should have been a great run. I was defeated instead by my head and my heart, which is more discouraging than physical ailments

However, I am a runner. I am a marathoner. I just have to figure out how to shake this training slump I seem to have drifted into in the past few weeks, and I will be more confident in shouting those two things from the rooftops. Any tips on how to shake off runner's malaise and/or negative thoughts?