It often happens that people fall asleep during the Shabbat meal on Friday night. If a person falls asleep, and after he wakes up he decides to eat some more food, must he recite new Berachot? Seemingly, his nap constitutes a Hefsek (interruption) which negates the original Beracha he recited over the bread, such that he would have to recite new Berachot over any food he wishes to eat.
The Shulhan Aruch addresses this question in the Orah Haim section (178:7; listen to audio recording for precise citation). He writes that if a person sleeps a "Shinat Ara’i" (literally, "temporary sleep"), as opposed to a "formal" sleep, then he does not recite new Berachot when he wakes up and resumes eating. Of course, this raises the question of how to define a "temporary" sleep. The later authorities explain that if a person sleeps in a seated position, then we define his nap as "temporary" regardless of how long he sleeps. Since people normally sleep while lying down, we classify sleep in a seated position as "temporary." Therefore, one who falls asleep in his chair at the Shabbat table does not recite new Berachot when he resumes eating, regardless of the duration of his nap. It should be noted that he must wash his hands (without a Beracha), as is required whenever a person wakes up from sleep.
If a person went to lie down during his meal and slept, then he must, indeed, recite new Berachot when he wakes up and resumes eating. Halacha states that if a person lies down and sleeps for the period of time needed to walk one hundred Amot (approx. 200 feet), which is estimated as just one minute, then his previous Berachot are negated. Therefore, if a person retires to the couch during his meal and sleeps, even for just a few minutes, he must recite new Berachot when he returns to the table and resumes eating. Of course, as mentioned earlier, he must also wash his hands (without a Beracha) just as one must anytime he sleeps.
Summary: If a person fell asleep in his chair during a meal, when he wakes up he must wash his hands without a Beracha, but does not have to recite new Berachot on the food he eats. If he fell asleep while lying down on a bed or couch one minute or more, then he must wash his hands and also recite new Berachot on the food he eats upon awakening.
