I second the visualizations advice, before a dive run though the entire process from gearing up to climbing back up that boat ladder. It should calm you down and allow you to think about possible problems/solutions that could occur underwater.
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Lets see: drowsiness, lightheadedness, tiredness, dizziness, irritability, talkativeness, dry mouth, increased salivation, difficulty urinating which of these are a good idea for diving?
Those are NOT guaranteed to happen. How could you have dry mouth and increased salivation?
Obviously you would want to take the drug and test it on your system before you dive.