Fear, greed and hope rules markets more than fundamentals. Computerised algos often search the news and aggregate concerns about a crash. They utilise this information in making decisions on whether to short or go long. I just checked Google Trends only to find that searches on 'market crash' are rising in the last week. Not surprising. The recent two peaks of concerns were in Oct and December. If this continues, and the algos get involved I'd be expecting more trouble.