Do you spend a lot of time on the computer? I counselled someone a while ago with a similar problem to switch off his computer and go outside and play, and after much deliberation and trying of many other things, he finally did it. A month later he e-mailed me to say like wow, that was totally it!
I have sorta the opposite problem to you though... no matter how shattered and exhausted my body is, my brain drives it with big whips and stuff, relentless... relentless... can't sleep, can't sit still, must pursue ideas... I'm like the Pink Panther in that episode where the fly gets into his room and won't let him sleep. The fly in my room is my infernal, inexhaustible mental energy.
But anyway, back to you - J's generally tend (it's my observation) to like to be 'people of action', people of their word. Specially FJ's - they need to know (and sometimes have it known) that they live by their beliefs, their values, their principles. The IFJ's I know can be prone to sometimes taking too much 'alone time', namely with that thief of all time, the Internet, and thereby making of themselves a Person Who Does Fuck All. It makes them lose their self-respect a bit, which affects their motivation a lot. Switching it off and going out and doing some stuff you believe in, rather than spending time telling strangers that you believe in it, often works wonders.
Dunno if that applies to you, just a wild stab in the dark, since you haven't given me much to go on.