Are you an extremely active person? Do you lift weights and/or do
30-40 minutes of aerobic exercise every day?

You might be cutting your carbs too low. Try adding more healthy carbs
in the form of veggies, low sugar fruits, and whole grains. Whole
wheat spaghetti, whole grain bread from the health food store, brown
rice, old fashioned oatmeal, etc. etc.

I'm a stay at home dad and I do a lot of running around, picking up my
baby and changing her, housecleaning, etc. I had the same problem. I
lost a lot of weight but I also felt like I was going to pass out
sometimes. Basically I depleted all my glycogen.

Find a balance that's right for _you_ so you lose weight without
losing energy. Everyone's body and lifestyle are different. (On the
days when my wife has the baby I eat a lot less carbs!)

"Atkins for Life" has good advice on this topic and I think South
Beach covers it, too.

eat a bit less, exercise more for stalls. it isn't what you want to
hear, but it's what will work.

I'm an At-kid but that's close enough for this purpose.

That's common early on in low carbing.  Some adjust back in energy
levels in about two weeks even if they stay on the lowest phase.
Almost all adjust back in enery levels quickly once moving on to the
next phase.  So you may do fine just by waiting 2-3 weeks, your
chances are much higher if you continue on through the steps.