After being released from hospital my mother is having breathing problems all the time?

My mother is 58 yrs old. Recently she had dengue and was admitted to hospital. After being released from hospital she is having breathing problems all the time. We consulted doctor and got to know that all sort of tests came all right.. there is no problem found… she is taking medicine also for the breathing problem and again got admitted to hospital and was given oxygen there. Now she us at home but the problem still persists. But doctors said there is no problem, no heart or health problem at all.. it is happening due to anxiety.. my question is if that is the reason then why she is having breathing trouble all the time all throughout the day.how can it be cured.. please advise

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