Travel and mood are very much related. Often a trip is associated with a significant change in mood. This can be due to many factors. Getting out of a rut, experiencing new locations and meeting new people can bring you out of the depression. However there is also the possibility that travel may disrupt circadian rhythms in a way that leads to a change in mood. There are at least two studies (see references below) that examined the relationship between the direction of travel and presentation of patients with psychiatric emergencies in airports. One in London and the other in Honolulu.
The study conducted at Heathrow airport suggested that eastbound travel was associated with hypomania or mania and westbound with depression. In this study the association of westbound travel with depression appeared to be stronger. However the study did not consider how these presentations compared with presentations of other patients having psychiatric emergencies. In other words it didn’t evaluate whether patients having psychiatric emergencies were more likely in general to have depressive or hypomanic or manic presentations.
The table at right illustrates the findings from the study in Hawaii. In this study the association between travel direction and mood was strongest for hypomania and mania symptoms in Eastbound travelers. Westbound travelers might have had 
slightly more depressive symptoms but when you factor in the control group which was a group of patients who hadn’t traveled you can see that in general people who present to an emergency center are more likely to have depressive then hypomanic or manic symptoms and so the association between westbound travel and depression doesn’t look to be significant. On the other hand eastbound travel was very strongly associated with hypomania or mania.
In addition, since seasons, particularly Spring and Fall, are often associated with mood changes in people who have a mood disorder, traveling from one hemisphere to the other, which naturally involves moving from one season to another, can lead to mood changes. If you’re in the midst of a fall or winter seasonal depression and you go to the southern hemisphere you may switch from depression into a normal mood or even into hypomania or mania.
And this is likely to be particularly pronounced if you’re going from an area that has naturally cloudy weather to a particularly sunny location.
An older retired man who loved to travel to sunny locations in the winter have a great deal of difficulty avoiding becoming hypomanic, which would ruin the vacation for his wife traveling with him.
What can you do about this? Do you just need to stop traveling?
We have elsewhere strongly recommended that people use the jet lag calculator on the British airways website to make appropriate adjustments in light and darkness during and after their travel in order to most quickly accommodate to the new time zone. This is particularly true if you are traveling east because eastbound travel seems to be associated with more severe jet lag generally.
This is a link to that site.
This should be adequate to help prevent depression, but in those who are traveling east and who have some risk of hypomania or mania it may be a good idea to carry along a medication to ensure that you get plenty of sleep in your first few nights, since adequate sleep is one of the best preventative’s for hypomania. In addition, sleeping later then you usually do is also a good way of preventing hypomania and this generally fits with the recommendations from the jet lag calculator which encourages you if you are traveling east to avoid light until later in the day.
References
Jauhar P, Weller MP. Psychiatric morbidity and time zone changes: a study of patients from Heathrow airport. Br J Psychiatry. 1982 Mar; 140:231-5.
Young DM. Psychiatric morbidity in travelers to Honolulu, Hawaii. Compr Psychiatry. 1995 May-Jun;36(3):224-8.