We get tired shuffling the cards ...?
LOL
Drained reiki(spirit energy) is a problem for new students to the Tarot, supposedly. I, too, felt my energy drain away from me when I was new to this and when I did huge, confusing spreads for my friends. And I agree, analyzing the cards used to take a lot out of me too (once you're accustomed to all the cards' meanings, it'll get better). Huge spreads like the 10-card Celtic Cross drained me. This prompted me to revise the Celtic Cross, make it make sense.
new CC here:
http://www.tarotforum.net/showthread.php?t=71839
One time, I was reading the tarot cards for my friends at Starbucks cafe and right after so many readings all at once, I saw stars and positively was on the verge of blacking out. My friends were a bit worried, said I needed some sleep.
Also, I've heard from a fellow tarot-student that you can, in fact, do nothing but read Tarot for a while and feel absurdly tired all day despite not doing any strenuous physical activity, which led me to conclude: twas' the brain that got tired. You know? Using psychic muscles that we usually use? Like MercyMe put it, "the more we use our psychic muscles, the stronger they get" -- or something to that effect.
True to her words, I stopped feeling drained after some months with the Tarot. The mind muscles get stronger, become less easily tired out.