Real losses or paper losses?
If OP puts tax-deferred all into bonds, he is at about 60/40. Stocks dropped 50% three times in the last 50 years. Bonds have dropped 20% once in the last 50 years. With those drops, a 60/40 portfolio is 30% at risk from the stocks and 8% at risk from the bonds. I would not worry about putting the whole bond allocation into Total Bond or into an Int Treasury fund. Now is a good time to do that while stocks are near an all time high and bond funds are still down a bit, but paying good interest rates.