Start with a patient list on one worksheet, just patient names and/or identifiers. That is, a unique identifier to identify all of the patients that you want to track, whether that is by name or patient number or whatever.
On another worksheet, use the patient name list as data validation to list the patient names again, with separate rows for each patient + his or her ailment. For example, if "Joe Blow" has kidney stones, cancer and a heart condition, then you'll have three rows of data:
Joe Blow Kidney Stones
Joe Blow Cancer
Joe Blow Heart condition
In column C:C of the same "listing" worksheet, concatenate each patient and that patient's ailments, so:
Joe BlowKidney Stones
Joe BlowCancer
Joe BlowHeart condition
On your main sheet (and I haven't done this with a form, so I'm not certain of how the technique might change), use your list of Patient Identifiers again as a Data Validation entry, so that you'll choose patients by their name or other identifying value. In the adjacent column, the working formula will be something like:
=IF( LEFT( 'Patient Names and Ailments'!B2, LEN( $B$3)) = $B$3, 'Patient Names and Ailments'!B2, ""), copied down the sheet so that it will be sure to look at the entire list of patient names and ailments.
When you have that arrangement set up, then you can filter on the list of ailments for the selected patient (be sure to not show blanks) or use that - as I think you want to here - as a form of data entry / validation.
I hope this makes sense, because it's been a long time since I did this, and it's possible that I have left out some steps.
