I fear I have begun my post without reading thoroughly through the preceding posts. I have since read them, but I just wanted to say that I agree with much of what has been said. I hope I don't sound like a windbag repeating things!
The concept of tarot cards is that they should be used as a tool, much the way you would use a screwdriver or hammer. You can gently tap a nail in with a hammer and your nail will go exactly where you placed it, no cracked plaster, etc.. However, if you put too much force on the hammer, you may bend the nail or break the wood, or even the hammer itself.
In other words, I don't think that tarot readings should be draining you on a supernatural level. They are cards which, theoretically, are connected with the thought and feelings within us and, hopefully will bring to light the innerworkings of a situation. They are not "charmed" or blessed with any special powers. Even the noted psychologist Carl Jung used tarot to put forth the idea that it is basically our subconscious mind cluing into these things we cannot physically see or understand.
However I know from my own experiences that I had done readings where I desperately wished and hoped and "needed" a certain answer to be "yes" when really it was a "no". I just wouldn't give up, and eventually, when your brain thinks that it wants something badly enough, it can actually carry some control over the cards, and have an adverse effect on the veracity of your reading.
With tarot cards, the main things to focus on are calm concentration and paying attention to not only the word descriptions of what a card means, but also to take note of the cards themselves, the colors, the immediate feeling you have upon seeing them. And never ignore those cards that jump out uninvited! They've got something to say and want to be heard.

You must take the background meaning and meld it with your gut instinct about the card you see before you, and the story it tells, all the while being careful not to kid yourself into thinking something untrue.
I could be wrong, because everyone experiences these things in different ways, but overall, I think if anyone is feeling drained by the experience it may be that you are bringing far too much blind worry into the question-asking. Maybe your question concerns something very serious, leaving you in a heightened mental state. You must face your fear regarding your query, and accept what you are most frightened of before having the courage to accept the truth which may ultimately be revealed.
The only other explanation I have for any sort of fatigue or drained feeling is some people believe that there are spirits that will try to speak "through" you, just as if you were using a ouija board or automatic writing. I don't really buy this explanation on tarot cards themselves, but I am open to anything. (The joy of a mysterious science....nothing is written in stone!) However, if you feel anything strange or "off" where you are doing your tarot readings, perhaps you should take care, just to be safe. White candles are always good, crystals are good if you're into that sort of thing, but basically you must feel comfortable and calm and that there is nothing "bad" with you in the room. Again, I think this phenomenon with tarot is less likely than in other more "direct" ways of communicating with other worlds.
Someone also mentioned tuition and feeling about spreads. I touched upon the intuition factor, but being comfortable with spreads are important, too. For example, I find the celtic cross spread to be confusing at times. I have two different books that show the same celtic cross spread, but with different interpretations for the crossing card or the near future card, etc. In these two books, you may have one spread, but the descriptions for the placement of the cards will result in two astoundingly different answers. Which do you believe?
Tarot is very versatile. You can be creative with your spreads and design your own according to your own needs and queries.
Sorry for the blabbering! I just don't get to talk tarot too much. ;)