Spotting 1st time in week 18 :(

Hello, I just stepped into 18th week. I've never spotted before ever since I conceived. Today I noticed brown discharge on my panty and a little more as I wiped with toilet paper. It happened late in the night, called up my doc and she has asked me to visit her tomorrow morning. It is scaring the hell out of me. Anybody else who has experienced similar thing, but had a healthy pregnancy?