I've been taking my bbt for the past 18 months and sometimes your bbt will go way down as a sign of ovulation, although it's what 5 days after the positive opk? I agree with kikicoates... the temp could be a fluke, just check it again tomorrow... I'll have a random really high temp or a really low temp and it doesn't really mean anything...
Well I couldn't see any charting so I can't say 4 sure. Are you temping correctly? Are you being consistant ~ b4 you get out of bed temping? Have they been up for several days? I would just re-temp tomarrow morning to see what the deal is.