Wow... this thread might explain *a lot* for me! for past 3 or 4 years Ie been to about 5 different GPs, had countless blood tests, ECGs etc etc and all have come back fine...none of them could explain why I was so tired all the time, and have always been pretty fatigued..... about 3 months ago I went for a sleep study (after a month or two before, talking with a sleep specialist) ... well... as you can expect the sleep study did not go well, there was anxiety.... but then.. there was *pain* from the leads and chords on me everywhere - it was like an un-ending nightmare! (ended up with a rash and bruises from tape and lying on chords - which I had for 5 days after) I was there for the night and the whole next day doing sleep studies.. and had barely slept the night before... the test started at 9pm. At about 5 am I fell asleep lightly - off and on, for about 2.5 - 3 hours - from pure exhaustion (was crying at this point) ... anyway the results of the test were pretty useless, and the results from agtigraphy watch (monitors light and movement) I wore for a week showed that in general I got about 8 - 8 and a half hours sleep.. and was getting a fare bit of deep sleep... which left me shocked (as I feel as though I dream *the entire night*) .. (I understand that its usually only an hour or so of REM and seems longer.. ) but some mornings I wake up and tell my boyfriend about my dreams I had that night... (which ends up being 3 to 4 long dreams in a row which are highly detailed) takes me an average of 15 minutes of solid talking to describe a simple version of all the dreams...but most mornings I have immense trouble waking up, and have had to resort to a bar-code scanning alarm clock! haha (alarm wont stop until you get out of bed and scan a QR or bar-code on the bathroom mirror), then takes me a good 2.5 - 3 hours to be able to take things in and not want to fall asleep again.
I usually wake up and am able to focus (sort of) from about 10.30 - 2.30 then crash in the afternoon a bit.. but stay awake, am tired from 3.00 - 45.30 ish... and then from 8 - 10.30 / 11.00 pm am okay... then crash and go to bed.

Also have trouble with physical fatigue, I am very un-fit but a normal weight - climbing two flights of stairs has me so tired! and if I have to run for my train (5 minute run) I have to use asthma puffer and takes me a good 15 minutes of sitting down to get my breathe back to normal :/

Perhaps a lot of the tiredness (at least during the day) can be related back to Sensory Problems and feeling over-whelmed