Should I be guilty taking sick leave under a hourly rate?

No one should feel guilty about it although I understand the feeling. I used to feel super guilty about it when I was a teacher because it was such a hassle for a school to get a cover teacher in, they really made you feel bad. But one time I tried to struggle through what ended up being a real bad infection. I worked for 3 days feeling rubbish but it got to the point where my class of 6 year olds were telling me I needed to go home and eventually the school receptionist sent me home in a taxi. I went to the GP and they were not impressed, was put on antibiotics and told to rest for at least a week, got signed off and had to attend another appointment before they'd certify I could return to work. And all I thought was, if I had just taken the time off as sick initially, I probably wouldn't have been in such a bad state! So yeah, that's why I now take sick leave even if it's not too bad, because chances are you can't work productively and you'll just make yourself worse! Better to take a couple days to recover than to struggle through, produce sub standard work and then make yourself really unwell.