I seem to feel we've had this conversation before.
Are you on NovoMix insulin? I ask because I had to stop it rather rapidly as I was having regular hypos, then rebounding to very high figures in between - beyond the reaction to the hypo treatment, which I started treating conservatively when I saw the high numbers I was also getting. As soon as I stopped it, I haven't had a hypo since. I was fluctuating between about 3 and 19 within a couple of hours.
I found that the background/basal aspect of it (70% of the mix) which is intended to last around 12 hours in your system, was for me, lasting about 16 hours. Therefore when I took a dose with either my evening meal or breakfast, after about 4 hours I was having a hypo as I found that I had effectively three doses of insulin active - the 30% rapid element for my meal was still active, the 70% basal of the recent dose was just reaching maximum potency and the basal aspect of the previous dose was still working, hence hypos at 16 hours after the previous dose and around 4 hours after the most recent.
I've since changed to Lantus and NovoRapid so that I can tweak the different elements individually and am much more stable and consistent on it. My research would suggest that mixed insulins are good short-term for getting wayward diabetics under better control, but not as good for long term maintenance once your numbers are lower. My range now is still a bit high, as we're titrating the dose up, but between around 6 to 10 - but on less than half the dose of the mix I had been taking.