Before giving a definite answer, it is important to know in which posture you normally are when meditating, and what you are habitually thinking, feeling & behaving minutes to hours before.
When you're lying down then obviously your body will think it's time to sleep. If you ate a lot, you will become sleepy due to the dgestive activity.
You also have to realize that practise is preferably done as much as possible, that is, (i) to prevent & to abandon unwholesome state of minds; and (ii); to bring to existence and to strengthen wholesome state of minds. This is right effort.
Rigjt effort is that important because whatever you think and ponder upon frequently, of that will be your inclination of your mind.
"Whatever a monk keeps pursuing with his thinking & pondering, that becomes the inclination of his awareness. If a monk keeps pursuing thinking imbued with sensuality, abandoning thinking imbued with renunciation, his mind is bent by that thinking imbued with sensuality. If a monk keeps pursuing thinking imbued with ill will, abandoning thinking imbued with non-ill will, his mind is bent by that thinking imbued with ill will. If a monk keeps pursuing thinking imbued with harmfulness, abandoning thinking imbued with harmlessness, his mind is bent by that thinking imbued with harmfulness.
So if you have been negligent in your daily life regarding the five hindrance (no offense here, it happens to all of us), then naturally the hindrances will be quite strong during a formal sit.
This is precisely the reason why kammatthana ('place of work') refers to the continous work of weakening of the five hindrances, and the strengthening of the seven factors of enlightenment.