I came across this thread about INJ's and tiredness at MBTICentral:
http://www.mbticentral.com/forums/mbti-enneagram-other-personality-matrices/7289-injs-you-tired.html It really spoke for me as I often feel tired - and I mean physically as well as mentally and emotionally. I actually cannot remember the last time I felt wide awake and fully refreshed.
Maybe this is a consequence of being INFJ? I know I find the modern world to be utterly exhausting at times, since there seems to be very little time or approval for the quiet activities which recharge my batteries. I often wish my workplace had a "Quiet Room" with comfy couches (or even beds) for resting, meditating, snoozing or daydreaming.
I'd write more on this subject but I'm so exhausted my eyelids are starting to droop, so I'll just hand it over to this community for your views (if you're not too tired to type!)
(Yawn.....ZZZZZZZZ)