5. You (not be) so tired if you (not work) so hard.

This sentence describes a hypothetical situation in the present, indicating a second conditional structure.

The first blank requires the past subjunctive of 'be', which is 'would not be'. The second blank requires the past subjunctive of 'work', which is 'worked'.

Therefore, the completed sentence is: You would not be so tired if you did not work so hard.