The first step to reducing this stress is to learn how to manage it.
I once worked for a large technology company and became inundated with work and was often overwhelmed with trying to decide what to do and when. My boss eventually sat me down and showed me a great exercise to perform every morning which can put you back in the driver's seat; by organizing your day and ultimately eliminating unnecessary stressed.
I like to call this exercise the 'Priority Matrix'
To perform the priority matrix, either pull up your favorite spreadsheet on your computer or just grab a pen, and a pad of paper.
The first thing we are going to do is write down all the activities you need to do in the day in no particular order. If you are working, list all clients you need to call, any paperwork or activities that need to be performed in the office and anything else that you need to accomplish. Once you can visualize everything you need to accomplish, we need to prioritize these jobs. Things that can wait a day or two to finish should be placed closer to the bottom of the list, and the more urgent items should be placed at the top.
Once you've organized your list based on the more immediate priorities, start from the top of your list, and do each activity until it is completely finished. Jumping from one activity to another without completing it deprives the designated activity from the attention it deserves and lowers your quality of work.
If you manage to finish all your major priorities, you can now start chipping away at your lower priority activities and possibly begin reducing your future work load by completing work early.
If you do plan on practicing the Priority Matrix, make sure you do this each and every morning. You will notice an immediate source of stress relief knowing that there is some order to your day; as the jobs are removed from your list you will begin to see the light at the end of the tunnel much more clearly than if you just winged it all!