I agree with Hurdity - even a half hour walk a day would be helpful. This should be about two miles and you can build up from there.
As for the horrible hot feeling - yes this, in my experience, is a daytime flush/sweat. Some women (such as me!) get them regularly - say every half hour or so - throughout the day and night. They can make you feel quite ill before you realise what they are. Before you begin to feel hot you various sensations can assail the body. Heart rate can increase, a feeling of doom and tiredness comes out of nowhere, then a queasy feeling in your tummy before the heat starts to build. Mine used to last around four minutes and, in the end, they were happening every twenty minutes. I could set my clock by them and learnt to go into the supermarket for the weekly food shop just after one hit, race around and be at the frozen food section when the next one hit. Then it was a race to get through the checkout before the next one. This, and the fact that I was finding it increasingly difficult to do my job, is what drove me to start HRT and the only thing I was annoyed about was that it had taken me so long to actually make that decision. My life improved immeasurably after that.
Taz x