One thing that is different about magnesium oil and sea minerals from other types of magnesium supplements is that they have calcium in them. It may be either that you already have too much calcium or the opposite - you may have so little calcium or not be able to absorb it in your digestive tract and so your body makes a lot of the enzymes that use calcium and a sudden rise, even if it is a little bit, causes symptoms as those enzymes go to town until they have time to adjust.
In the first case you would want to avoid magnesium oil. In the second case you would want to gradually build up.