Ha! I get real pre-hike anxiety, but it is not something just drummed up in my mind. In my case it is a serious case of "what am I forgetting to pack?", since out on a multi-day trip, one has to take everything required to survive -- food, clothing, shelter, emergency needs like first aid and wet weather gear.
Leaving out one key item can make for a really miserable part of the trip.
I've run several marathons, and never did I experience the pre-run anxiety like I do before a big backcountry trip.
Things I have forgotten in the past:
Bread or pita bread. Substituted bagels.
A second lighter or matches.
Things I fortunately took along on several trips:
Air mattress patch kit (bicycle tube repair and duct tape) -- for a NeoAir punctured by a pine cone needle.
Credit card, cash, cell phone: Last summer after my car was made unavailable by a forest fire.