Always do some walking meditation before sitting, especially if you know you're feeling sleepy. The Benefits of Walking Meditation
Both Venerable Moggallāna and Venerable Ānanda gained Arahantship on the back of doing walking practice for long periods — seven days and nights in the case of Venerable Moggallāna,¹ and the whole night in the case of Venerable Ānanda.²
¹ This is said in the Commentary to the Pacalāyamānasuttaṃ, which relates how the Buddha noticed in his divine eye that Moggallāna was nodding in meditation, and so came to where he was staying to teach him. No wonder he was sleepy, since he had been striving for seven days since his “Ehi bhikkhu” ordination to win the final goal, by practising walking meditation strenuously.
² This occurred on the eve of the First Buddhist Council to which Ānanda was invited, but since he was still a Stream-winner, he practised walking meditation the entire night and gained Arahantship at dawn, after going to take a short rest to balance his mental facilities.