I have never been to Alaska but I have been in Finland and Sweden and Norway although not diving. Even during the day the sun does not get directly overhead. I am guessing that would also reduce the amount of light that penetrates to depth. If that is the case it would be another reason to use a small light sometimes during the day.
The sun may not get directly overhead, but this time of year it is hard to get a decent nightdive in Norway without staying up untill the wee hours.
But, to get back on topic...
Knowing exactly what you talk about... drysuit... Algae... murky cold waters... what I theorize is the problem here is really your breathing.
And it surprises me slightly that ppl have not mentioned it before.
With a drysuit, a hood and heavy gear everything gets heavy and cumbersome. This increases the need to ventilate CO2, but decreases the bodys natural ability to adjust breathing pattern to do such a thing. Being anxious and very often breathing "on the top of your lungs", but at a elevated rate will further diminish your bodys ability to expel CO2 from the lungs.
CO2 has a very narcotic AND anxiety enhancing effect, and your breathing pattern might very well be what is the reason for your troubles.
I really do not understand this SB tendency to advice all divers that encourage trouble to "Go somewhere warm and fuzzy"... Very often there is a good explanation to the problem people are experiencing.
I normally dive in Norway. I dive all year round, and there is no such thing as a "dive season". Drysuit all year!
I would like to challenge you. Find a favourite patient buddy. Plan a series of dives over a weekend, or afternoons during the week. For each dive, you challenge your own comfort levels. Dive #1 Descend to 15 feet. Find a small patch of "anything that grows". Lay still and focus on hovering over this patch. Keep focus on your breath. One trick I did to remember to do good exhales was to take short inhales, counting to three, and longer exhales, really expelling the air over a count to 6. Keep breathing. Keep focus. When you feel you are breathing good, take a minute, and check if you feel that anxiety feeling.
Dive #2 Descend to 25 feet... Do the same
Dive #3 Descend to 40 feet... Do the same
And then on...
Make sure you feel calm, and know that your breathing is purposeful before you go on.
Edit:
Oh... And you are NOT a nervous nellie for calling a dive when you have had enough. ANY diver can call ANY dive at ANY time without ANY reason!!
Remember, low viz, cold water and drysuit will all tax your concentration. It takes time to "exercise" this capability, so maybe a good idea would also be to plan shorter dives so you would not experience getting exhausted and had to "call" the dive.