There's loads of things to worry about if you are a bear such as valuations, China, US yield curve flattening, economic woes in Europe, the recent collapse in freight rates etc. Here is an apt summary of these views from the pro's:
Things to Worry About as a Bear
Every So Often Ben Bernanke Reminds Us Why Economists Are So Dangerous
-
To say economists disappoint surely flatters them.
42 minutes ago