It could be the mercury detoxing causing the symptoms, but I thought I'd mention a few things about chlorella just in case symptoms persist.

Chlorella contains high amounts of iron. If you're extra sensitive to mercury (which I'm guessing you are) you could potentially be sensitive to other metals such as iron, chromium, zinc and so forth.

Chlorella is rich in chlorophyll which again contains high amounts of vitamin K. This vitamin coagulates blood so could make your blood sticky causing symptoms such as fatigue, brain fog and flu-like feelings.

Chlorella packaged in aluminium foil could potentially contain alu from the wrapping.

Chlorella is very high in vitamin A (beta caroten). If your liver is compromised it will have problems detoxing vitamin A and cause a build up resulting in a toxic feeling.

Because of the above reasons I use Chlorella infrequently and make sure I take a kind of blood thinner when I use it. Such as garlic, ginger and bromelain (pineapple enzyme).

Chlorella is great for chelating the gut of metals, but will not chelate the nervous system. Neither will garlic, ALA, Algin or vitamin C. Some of them only mobilize/move mercury around, but will not remove from the brain area. Most of the bodily problems associated with mercury poisoning such as digestive allergies, fatigue, aches and pains and of course all the mental symptoms originate from a poisoned, non-functioning hypothalamus and pitiuary gland. These as VERY important to chelate in order to rid yourself of all the other symptoms. The hypothalamus also controls the adrenal glands which in themselves can cause a whole list of symptoms if the hypothalamus isn't able to send the correct messages.

Cilantro will actually remove mercury from the central nervous system. ALA mobilizes in the CNS and DMSA grabs hold of the mobilized mercury. Other chelators I have no experince with.

Hope this helps some

PS. If you're concerned about mercury in the gut getting redistributed, I highly recommend using a very high fiber bran cereal (with water not milk as calcium will prevent detoxing). Studies have proven that this kind of fiber binds with hg in the gut.