It's not tiresome and not a silly question.
Some people find that when they start meditation practice, they fall asleep, so it's not unusual and not wrong.
Things you can look at for your practice:
Ensure you are sat comfortably, with your back supported if necessary, but don't use a chair that supports your head as this is tantamount to lying in a bed and you will be too comfortable and easily able to fall asleep. If your head isn't supported then if you start to fall asleep, usually the dropping of the head will bring you back to alertness and allow you to continue meditation.
Check what time you are practicing meditation. Often, meditating when you first wake up in the morning will not only be a good way to start the day (as you often feel more alert after meditation) but as you've already had your sleep you are less likely (well for some people anyway) to fall asleep again, especially if you've already got yourself out of bed, walked about and gone to your place of meditation. Meditation right at the end of the day, before going to bed is more likely to be when you are tired and more likely to want to naturally fall asleep. For my meditation practice I usually do it first thing in the morning and then after returning from work before eating in the evening (eating is something else that makes the body feel tired as your energy gets directed into digestion)
Also consider how long you are meditating for. If you're new to meditation then doing a full 40 minutes of meditation (the lifeflow length for downloaded tracks, or 60 minutes for the bought CD's) could be more than you need at this time. People who just learn meditation (transcendental meditation style, like the mantra meditation Michael provides) usually start at about 5 or 10 minutes meditation and work up to about 20 minutes. It's usually more experienced meditators who extend meditation to 30 or 40 minutes. Maybe you just need to cut your meditation length to a shorter time for a while and then gradually build it up when you've practiced more.
All in all, there's no need to beat yourself up about it if you do fall asleep; it will happen occasionally. It's not unusual for people who've practiced meditation for some time, to find that they actually start requiring less sleep. Stick with it.