Do you want to lose weight or gain it ?

That wasted feeling is how you feel when your blood sugar is low (I think it's similar to the way that type I diabetics feel before a fit). When you're on a serious diet you feel like that a lot of the time (ugh...).
It doesn't appear to be a serious health risk to normal people, although of course it makes it difficult to get home.

1.2 L for 42 miles (~60 km) seems a little bit low, although maybe you live in a colder area than me (Australia).