Toprol-XL and warm environment

I was prescribed 25 mg Metoprolol-XL for irregular rapid HR episodes and slightly increased BP (after all the tests to rule out heart disease). It did the job, but I began to suffer with insomnia (a common side effect). So for the last month and a half, I've been only taking half the dose (I made sure that it was the type of tablet that was ok to break...it is, but they do caution you not to chew or crush it). No more insomnia, and the irregular HR has not returned, BP remains normal.
I figured out that the cause of the palpitations etc. was delayed anxiety attacks from a recurring family situation (the delay made it hard to link the cause and effect until I started journaling). Knowing that was the beginning of being able to better cope with the situation, so I thought I would be weaning myself off the medicine. However, I also am a migraine-sufferer and realized that I have not had to take an Imitrex since starting the metoprolol (3 months!). I used to get 4-5 migraines a month...now I may get none, one, or two and none so bad that one Ibuporfen can't handle it. Not so sure I want to stop taking it now.
New problem: Since cutting the dose, I find that any exposure to warm environment or to mild exercise, where I would normally only sweat mildly, if at all, now my scalp sweats profoundly, so much so that sweat runs rivers down my back, my chest, into my eyes and ears. The rest of me only sweats like I normally ever did. Is this because I decreased my dose...will it last forever? I did read that one should not go off this stuff cold turkey and that one of the things that would happen if you did could be excessive sweating. All I did was go from 25mg to 12.5 mg! What if I go off it completely...what am I in for??