Dragging myself through training

I woke up this morning feeling very tired and struggled to the pool for 6am. I tricked myself into an easy session suggesting only 100 lengths max. This worked and helped me through to 80. However, once I had hit that mark I was into the swim and I knew that I would hit the 120. What a gullible bugger that I am able to fool myself so easily.
Set out this evening feeling under the weather. Nothing specific, just feeling tired with a dull headache. I thought that maybe the run would clear my head. It didn’t but I was happy with the outcome 75 minutes reasonable pace, steady heart rate. I am finding it interesting how once I start running, swimming or biking, the habit takes over and I can perform far more effectively than I expected. However, I am very tired and am seriously wondering how I will manage the long bike and run tomorrow.