It is, especially in these markets where everything seems inflated. I have a ton of money in the stock market, and its' scary but I don't know what else to do. Every time I've tried to time the market, it's been an epic fail.
If your money is in a tax deferred account then reallocate some to non-equity.
If you'll be in trouble if your equities drop 50% then move some out of equities.
If it's in taxable accounts then you're stuck unless you can take the tax hit.
In any case stop buying equities until you reach a decent allocation.