No one knows for sure where Patrick spent his time in slavery but based on his letters there's a very good chance he was on the west side of the Island, in the coldest wettest region of Ireland. Tending sheep would have included bringing the sheep out to pasture, keeping watch over them, and bringing them in to safety in the evenings. He would have most likely spent his evenings in a shack of sorts with all the other slaves. He says in his letters that he prayed and fasted regularly and he made a point to never engage in any pagan rituals or activities. For example, often times food would be dedicated to a pagan god. Patrick would then refuse to eat such food; just a small example. The other slaves mocked him and would call him holy boy. But he never felt so close to God and never had such a strong resolve to dedicate his entire being to Him.
One night while Patrick was asleep he had a dream in which someone told him to get ready, that it was time for him to leave. The next night he had a dream in which he was told to, "go. your ship is waiting for you." Patrick was certain that this dream was from God and so he left. After spending so much time in prayer and fasting there was no possible way that Patrick was going to ignore a message from God no matter how dangerous the message was. A runaway slave would have been a fugitive and would be severely punished if caught. No one would harbor a fugitive runaway slave and anyone who found one would certainly return that slave to his owner. Patrick walked something like 200 miles through dangerous terrain as many, many an Irish traveler lost their lives to the bogs of Ireland which Patrick would have had to cross. When he did finally make it to shore there was a boat preparing to leave. Patrick walked up to the captain of the ship and asked if he could come on board as a deckhand. The captain said, "no possible way, and walked back on board." Patrick escaped from slavery. Walked a very arduous journey across Ireland and now when he was about to escape for good, "no."
He says that he wasn't sure what to do but right before the boat was about to leave someone from the ship ran up to him and asked if he was still interested in working on board. He of course said yes and joined the crew. Theory has it that the captain knew instantly that Patrick was an escaped slave. He would certainly have looked like a runaway. He would have spoke horrible Irish with a terrible accent. And no one would be caught dead harboring a fugitive slave. However crossing the Irish sea was hard work and if he took a willing laborer on board right as they were departing who would know the difference.
It took a little while and it wasn't an easy trip but Patrick made his way home. His parents would have been in shock to see him alive 6 years after he'd been captured. It was miraculous to say the least that Patrick escaped slavery in Ireland.
But it was here in Ireland that God first opened my heart, so that - even though it was a late start - I became aware of my failings and began to turn with my whole heart to the Lord my God. For He looked down on my miserable condition and had compassion for me, young and foolish as I was. He cared for me before I even knew who He was, before I could tell the difference between right and wrong. He protected me and loved me even as a father does his own child.
Because of this I cannot - I will not - be silent. I will tell of the great blessings God has granted to me and the grace He has shown to me in this land of slavery. Because this is the way we should behave toward God - when He has shown us why we were wrong and we have admitted our sins, we should praise Him and proclaim His kindness to everyone in the world.
-St. Patrick, from his letter titled "Confession"