It sounds like you had a very rough, sad evening. Do you feel responsible for the fight with your 17-year old? I am just wondering because I have four teenagers and mine are able to manipulate my emotions easily and make me feel awful for the way I react to a given situation. Adding this with bp symptoms that are not in control definitely adds to a feeling of instability.
Since you are with your 9-year old, maybe the two of you can watch a movie together-this will allow you some time to relax and maybe sleep a bit??? Be honest with your child letting him or her know that you are very tired and don't feel well and ask if he or she can suggest a quiet activity to do together.
As for feeling down, be kind to yourself. Don't let the sadness from the fight control you today. I know, easy for me to say, but it is possible if you can keep your mind from going there.
Many hugs!
Bluemountains