Father aged 90 years. Normal range.

My father aged 90 years has bn taking up his daily routine on his own regularly. Although his movement is not much but he moves within house on his own upto bathroom and for his needs for sitting, dining and sleeping etc. Recently since three days he feels acute weakness & trembleness in his legs restricting his movements. Earlier such problem was noticed 15-20 days back but it was associated with fever, however he is not having any fever. Possibly due to weakness, he prefers to sleep for extended hours due to weakness and talks in feeble voice. While walking or change in posture wheezing sound is felt in breathing although congestion is not felt. The food intake is ok. What medication / remedial is preliminary needed for him. He is regularly taking medicine for BP & constipation since long. Pathological tests CBC, urine etc are within normal range.