HI,
After over 20 years being Type-1, I wouldn't consider myself an expert by any means. However having experience of a quite a few differrent insulins, and a pretty lousy one on Lantus, I'd suggest that there lies your problem. For many people, including myself, Lantus can appear to be working ok for a while, then come the ups and downs and crazy unpredictable patterns (or rather no pattern!).
You may well be coming down with something, and time will tell. However if you continue with these fluctuations, your health will suffer. I was on Lantus for over 4 years, and had no control whatsoever. Nothing I did made any difference to BG levels, it just did it's own thing,and I followed, with a lot of corrective doses,which sometimes made no difference either. One day was never the same as the next. I tried to find a pattern, suchas my menstrual cycle,but there was no pattern. For me Lantus did not do what is says on the bottle! It didn't work. Having changed to pork insulin last May, I no longer have these problems,so It's cut and dried for me.
Aside from the crazy fluctuations, I suffered some horrible side-effects, which have since disappeared since changing coming off Lantus.
See how you get on,and if your blood sugars don't settle down into a manageable pattern, you will need to speak to your doctor. It's no way to live with ups and downs, hypos and hypers-you should be in control of your diabetes, not the other way round.
If you want further advice you should look at the IDDT website, they also have helpline telephone number.
Best of luck
Jus