If we are talking about friends and family, the best way to make them understand is to educate them. Tell them how it feels to be you. Allow them to ask questions, (But nothing too personal!) so that they understand what you are going through.
If we are talking about the great general public then I wouldn't waste my time (Personally). The chances of you seeing them again are slim to none and chances are, they dont really want to know anyway. They ask you because they think its the right thing to do and they feel guilty if they dont.
I hope your sleeping has started to settle down now. If you are crying a lot at the moment, that places a big strain on your diaphragm. Imagine having to hold a tin of baked beans in your hand with your arm raised for an hour... Your diaphragm probably feels the same way. A couple of days and your body should be back to normal