Work and sick leave

Hello. I’m after some advice. The nature of my job means I don’t work nov-feb inc. so we have come away for the winter. Despite taking it easy I feel rubbish today so have opted out of family walk and sand castle building. Was thinking…… if I was at work I would have still gone it. Taken energy drink and concoction of anti inflammatory and pain killers. Last year I worked over time and went in when felt rubbish and ended up relapsing (first one in 6 years after lemtrada). So I have decided that on days I feel rubbish I must not push myself. The question is this. How does that work with work. Do you phone in sick if it’s just one day here and there there won’t be a sick note. What do people do please. (The job can’t be done working from home) I have already decided I can’t do overtime. Just never called in sick before and unsure. Thank you all in advance.