HTML:
<input type="checkbox" name="stomach" value="1" />
<input type="checkbox" name="head" value="2" />
<input type="checkbox" name="feet" value="3" />

SICKNESS TABLE:
+----+---------+
| id | name    |
+----+---------+
|  1 | stomach |
+----+---------+
|  2 | head    |
+----+---------+
|  3 | feet    |
+----+---------+

PATIENT TABLE:
+----+---------+
| id | name    |
+----+---------+
|  1 | Bill    |
+----+---------+
|  2 | Susan   |
+----+---------+
|  3 | Mary    |
+----+---------+

STATUS TABLE:
+------------+----------+
| patient id | sickness |
+------------+----------+
| 1          | 2        |
+------------+----------+
| 1          | 3        |
+------------+----------+
| 2          | 1        |
+------------+----------+