Welcome to Just answer !
I am sorry to learn about your father's condition and I empathize with you and him.
Well you see feeling exhausted all the time, lethargic , lack of energy, unmotivated and dis-interested in daily activities along with withdrawn into a shell , all of these are some core features of depression.
So while he is already placed on escitalopram which is a very effective drug to be on but I will recommend that the dose of escitalopram is to be raised to 20 mg after 2 weeks on being on 10 mg / day dose , reason being 20 mg / day dose is the optimal dose of escitalopram which is most effective against depression.
So usually it takes at least 2-3 weeks for any anti depressant drug including escitalopram to start making significant improvement in overall symptoms of depression , so if this much time has elapsed ever since the start of drug and he is still feeling exhausted then the next step is to raise the dose to 20 mg / day.
Another important step that needs to be taken is that he needs to be started on some supplementary over the counter remedies for infusing some energy in him which include omega 3 fatty acids capsule , 1-2 / day , multivitamin ( especially vitamin b complex ) capsule, 1-2 / day.
So to summarize--
-- His exhaustion is an extension of his underlying depressive illness which will get over once the depression starts to lift.
-- Ask his doctor to raise the dose of escitalopram to it's optimal dose of 20 mg / day so as to have faster relief from depressive symptoms including exhaustion.
-- Add necessary supplements like multivitamin capsules rich in vitamin b complex and omega 3 fatty acid capsules , which can be availed over the counter.
-- Have patience as it takes some weeks , say 2-3 weeks for one to start experience some positive changes in one's depressive features. If this much time has already elapsed and still no significant improvement is there then I reckon it is so because he is still not put on the optimal dose of 20 mg / day , so kindly do that.
I hope this helps.
Wish you all the best.
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