Yes – please inform your teacher if you have any medical issues or concerns such as new or pre-exisiting injuries or illnesses. Even if it doesn’t seem relevant to yoga, inform your teacher anyway; yoga can have a profound effect on every system of the body and your teacher may know of alternatives that will be relevant to you. 

For students that menstruate, please inform your teacher if you are menstruating (and which day of the cycle you are on, if you know); there are many poses which should not be done during menstruation and your teacher will give you alternatives throughout the class. You should also inform your teacher if you are pregnant and how far along you are. 

You can send any of this information in an email ahead of time.