More heart rate monitor oddities

Sunday morning run time again. I had to set off earlier than usual as the kids had an away rugby match to play in. I managed to do just under 7 miles in 1hr 2mins and 30 seconds, but yet again me and my Heart Rate Monitor (HRM) disagree.

As my morning run can be within 1/2 hour of getting out of bed I made point of doing some light warm up and gentle stretching for 10 mins before I started running properly. My HRM said 110 Beats/min OK I'll just about buy that. But then I started running and within 5 steps it was saying 162 beats/min. Nah something really strange going on here. After about 30 seconds it decided to suddenly change back to 150 but even this seemed strangely high as I was jogging on the flat. Now I know all the warnings about feeling faint and light-headed etc etc but I was getting no feedback from the rest of my body that anything was wrong. I'll keep an eye on this over the coming weeks.