One major culture shock for me was how different their times were. Breakfast was usually very light, maybe some yogurt or bread (untoasted, most times). Lunch would be after 2, very large, as they believe that lunch is the most important meal of the day. And dinner was at 10 or 11 pm, allowing for night life to thrive. Spain also has Siesta, where you spend time indoors from 2-5, as the sun is high and everything is super hot. It becomes very hard, especially for tourists who want to explore, to adjust to this new schedule. Thankfully, it is becomes easier as the time goes on.
One thing that helped me was, surprisingly, jet lag. I as was already super tired from all of my travel, that I slept the second that I could. Were the beds uncomfortable? Yes, but nothing that jet lag can fix, at least for the first two weeks.
What helped me with the different meal times were snacks, lots and lots of snacks. If you are with a host family, then they might have some snacks that they have for you, but they might feel a bit offended if you ask as they feel like they are not feeding you enough. Something that I found out. So, if you do want snacks, you could also just get something out of the house and eat it on your way home. Snacks, sleeping and sunscreen was all very helpful for my time in Spain.
The food is Spain is also very different from what we eat in the United States. To fight this shock, you eat it! It is all very good food, and tastes wonderful. Just be careful, inform your waiters if you have allergies! Mostly, to adjust to the culture shock, then you need to immerse yourself into the culture and have fun!
