I have this problem to the extent I thought I had a real problem...

Actually, I still might, but I digress...
The Ni-Ti loop sucks, but all the suggestions above are good. I would suggest:
- Stay away from caffeine. If I have two cups, I will not be able to concentrate on anything. At work, this has killed me. It was almost to the point of just needing to go home.
I can't even stare at a screen and see what's on the screen. Bad, bad...
- Exercise your Se, but do it cautiously. If possible, the hike idea or even a walk outside is a superb idea. It forces you to pay attention to your surroundings (especially on a hike.) But make sure you stay away from the bad side of Se. This part will suck me in very fast if I'm not careful. Smoking, drinking, spending, etc. Ah, Se..........
- Be with another person who can give you stimulus. Now before you go OMGOMGOMG, yes, it can be that kind of stimulus or hell, have them sing you a song or play with your hair or play a video game with you. You can tell a friend you're trapped in your own head and just need a silent companion. Oh, I freakin' love silent companionship. So wonderful...
-And what @
Hanne said. Planning something to do when it's getting bad is so key. Taking a day off of work to be ALONE, with NO PEOPLE... for me, that would be suicide. It seems like a rational thing, right? We need to fix things on the inside before we can present ourselves to the world, but that is the danger when we're stuck in that loop. *shudders*
Good luck!
(Also- apologies if I sound so damn preachy today. I hate when I sound like that, but on some days it comes stampeding out like a self-righteous herd of rams. I can't freakin' stop it...)