Work out the order in which you need to complete these tasks. Now allocate a time allowance for the completion of each task. Perhaps task 1 will take you 1 day to complete, task 2 may take 0.5 days, etc. Slot these tasks into the time you have allocated yourself for dissertation work on your calendar. By doing this you have set yourself a number of interim deadlines to complete each crucial dissertation task. The overall task in hand should now feel more manageable.