Can a lingering weeklong upset stomach be associated with whiplash or related trauma from being rear ended?

Yes!: Post trauma symptoms can occur days, weeks, months later and be tied into the vector or trajectory forces associated with the trauma, or seat belt restraints impact on the body. Also, any increased sympathetic tone to the fright or unexpectedness of the rear ending can affect the emotional tone present and give you upset stomach. See your PCP for further work up and treatment.