I had to call in sick today, and they gave me a bit of a hard time. Should I feel bad?

I work in a bookstore, and it's a pretty good job. I've been working there for about 3 months, and for the most part I like it. Sure, there have been days when I didn't want to go, but once I get there, the people are so awesome that I usually feel better.

However, this past week I've worked five days in a row, and by the end of this week I will have worked ten days in a row. Seven hour shifts, too.

Today I woke up with a splitting headache and a sore throat, and a massively overwhelmed/stressed feeling. Not to mention that I am SERIOUSLY overtired. After much deliberation, I decided it would be best to call in sick, since I knew I wouldn't be much use at the store.

This is the first time I've called in sick, and when I called and talked to the manager, she reminded me about the big visit from head office, and said they could give me a different day off. I briefly thought about it, but said that I really wasn't feeling well, and I wouldn't be much use. So she said that if I wasn't going to come in today, she would need to see a doctors note.

At first I caved, and said I would take some Tylenol and come in. But after hanging up the phone I had a bit of a breakdown. I called the doctor and made an appointment, and then called the manager back and told her that I really couldn't come in today, that I was sorry, and that I would bring her a doctor's note tomorrow.

I'm just feeling really guilty now, and as stupid as it sounds, I don't want them to be mad at me. Seeing as I had never called in sick before, I don't really know how it works. Do you ALWAYS have to give a doctor's note? Even if you call in sick for one day? Should I be feeling bad/guilty/worried? Or should I just think "it's their problem if they're mad at me"...
I had to call in sick today, and they gave me a bit of a hard time. Should I feel bad?
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