Why Did Inner Brow Drooped After Botox?

Medial brow ptosis or descent of the central brow can occur for several reasons and is often due to an inexperienced injector:
-Botox placed too low within the frontalis muscle along the forehead including central forehead.  The frontalis muscle elevates the forehead and by decreasing activity here the central brow can drop
-Botox placed too superficially along the corrugator.  The botox will again impact the frontalis muscle and paradoxically lower the central brow.
Botox is best injected by an experienced injector to lessen wrinkles while improving facial appearance.

It sounds like you had too much Botox injected into the frontalis muscle compared to the medial eyebrow depressors( the obicularis, procerus and corregators). The correction is the "Medial Botox Brow Lift" a small amount of botox into the depressor muscles to elevate the medial brow.

The position of the eyebrow and its shape is the result of a balance between opposing muscle groups. Muscles in the forehead lift the eyebrows. Muscles below the eyebrow pull the eyebrow down. When the lifter muscle of the forehead is weakened, the brow will fall. Depending on how this occurs, the muscles of the forehead that are still able to contract are recruited to lift the eyebrow. This is where those funny post-BOTOX looks come from. In some cases, the doctor has done such a through job freezing everything that nothing in the forehead can move. We see this effect in some of our actresses (think bat forehead) and gosh it is not a good look. But then who would tell Emperoress that she is not wearing any clothes?
Your treatment is at its maximum now three weeks after the injections. The effects will gradually wear off over the next three months. Find a new treating physician or encourage you current doc to avoid direct treatment into the forehead. Look at my microdropletTM BOTOX method on my website which describes my patent pending method of performing a BOTOX forehead lift.

You likely had a low brow in the first place, and by completely relaxing the frontalis muscle (the muscle which raises your eyebrows and causes horizontal lines in your face) your brow has dropped, as there is nothing to counteract this effect.
Sometimes, if this happens on the outer part of your eyebrow, we can successfully get that brow back up with a little more Botox around the eyes. Where you are experiencing difficulty is in the inner brow. This will be very hard to get back up. Your doctor may be able to place a little more Botox in your glabella (the corrugator muscles) to see if maybe they can balance this out, but it is doubtful. The good news is that the effects of Botox are reversible and will completely wear off gradually over time.

If your medial brow has dropped significantly, and you feel that it is very heavy or creating an angry look, you  may be better off with a brow lift at this point.