I HAVE A 1" FLUID FILLED SACK BETWEEN MY SKULL

I HAVE A 1" FLUID FILLED SACK BETWEEN MY SKULL AND SCALP. THE CYST OR WHAT EVER IT IS JUST APPEARED ONE DAY A COUPLE OF WEEKS AGO. I HAVE EXPERIENCED A 50% LOSS OF HAIR IN THE LAST 6 MONTHS AS WELL. I have a number of health problems so this fluid filled lump appearing out of the blue is kind of scary.