Not sure if the others have mentioned these, but try
Siberian Ginseng Rooibos tea Lots of water
And NO caffeine. I've had trouble with this issue too as I have Fibromyalgia (therefore muchos tiredness!), but I've found the hard way that my doc is right and I am better without it. It can take a hell of a while for your body to adjust though, so stick at it.
Being diagnosed with IBS means alot of things and one of them is that you are likely to have to alter your lifestyle. You can still study and do fantastic research, but not without sleep for days!
Yoga can also help with mental clarity. I know what it's like...although I didn't do post-grad study I did do a physics course here which was pretty heavy going!
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Re: The End Of My Career Without Coffee?!?I'm desperate.................
