Hi,
The biggest benefit to paying into an investment vehicle monthly rather than one off payments is that you even out these bumps in the market. When the price drops, your same monthly payment can buy more units than when the price is higher.
You need to ask what your aims are for this. If it is a long term investment - and I mean 5-10 years minimum - I would carry on (provided you are still comfortable with the funds that you have chosen). In years to come, when the price has recovered, you will look back on this time as the period where you got a real bargain.
Investments are not for the short term. As you have found out, these price drops can be very disturbing. Generally, the best thing to do once you have decided to invest in the stockmarket is to let it run its course unless something fundamental changes which causes you to reassess.
Hope this helps.
Just out of interest, what is the investment?