Hi Logan2
You would have been assessed on your condition(s) as you were at the assessment. Unless you had a paper assessment, last year you would have had a face to face assessment. The assessor would have taken everything into account, remember PIP is not awarded because of the condition but rather the limitations that result and prevent a claimant from completing a range of everyday activities.
Unless your condition has improved then you do not need to inform DWP of the outcome, when you are next assessed you will be able to say that you have been diagnosed with 'essential tremors', you will then need to explain how this condition affects you in completing everyday activities.
If your condition has deteriorated then you can contact DWP and inform them of a change of circs but this would trigger completing a new claims form and being re-assessed or you can wait until you are reviewed depending on how long your award was for.
Gary
Nothing on this board constitutes legal advice - always consult a professional about specific problems