Sudden cold shiverin with something more

My mother is experiencing sudden cold shivering attack in recent days. This happened thrice in last 2 months. The shivering comes along with some other problems like first two times there was terrible headache while on the third time terrible pain on left ankle with frequent (every 10-15 mins) pressure for urination. Every time this phase lasted for about 2 hours followed by weakness for the rest of the day and everything normal from the next day. The problem that I described above appeared just thrice in two months and lasted for about 2 hours each time. During the attacks blood sugar level remained unchanged, BP unchanged around 120-130/85-90 and little increased heart rate about 110-115. Can it be from some infection? But the problem is not persisting. Or what can be the reason for these. Please help.