If your physician has advised you not to wash your head in the morning, you ought to wash the rest of your body and skip washing your head, and perform a tayammum in lieu of the latter. Tayammum is symbolic ablution; it entails the following steps: Strike any clean surface with both hands; bloe off any dust on them and wipe your face with both hands; strike again, blow away the dust, and then wipe both hands up to the elbows.

Once you have washed your body except head and performed tayammum, you are eligible to pray. However, as soon as you can do a complete ghusl (including washing of the head) you must do so.