The soul is independent of any sickness or disability of body or mind

Know thou that the soul of man is exalted above, and is independent of all infirmities of body or mind. That a sick person showeth signs of weakness is due to the hindrances that interpose themselves between his soul and his body, for the soul itself remaineth unaffected by any bodily ailments. Consider the light of the lamp. Though an external object may interfere with its radiance, the light itself continueth to shine with undiminished power. In like manner, every malady afflicting the body of man is an impediment that preventeth the soul from manifesting its inherent might and power. When it leaveth the body, however, it will evince such ascendancy, and reveal such influence as no force on earth can equal. Every pure, every refined and sanctified soul will be endowed with tremendous power, and shall rejoice with exceeding gladness. 

- Baha’u’llah  (‘Gleanings from the Writings of Bahá'u'lláh’)

The “human spirit, unless assisted by the spirit of faith, does not become acquainted with the divine secrets and the heavenly realities.”

It has been before explained that spirit is universally divided into five categories: the vegetable spirit, the animal spirit, the human spirit, the spirit of faith, and the Holy Spirit.

The vegetable spirit is the power of growth which is brought about in the seed through the influence of other existences.

The animal spirit is the power of all the senses, which is realized from the composition and mingling of elements; when this composition decomposes, the power also perishes and becomes annihilated. It may be likened to this lamp: when the oil, wick, and fire are combined it is lighted, and when this combination is dissolved, that is to say, when the combined parts are separated from one another, the lamp also is extinguished.

The human spirit which distinguishes man from the animal is the rational soul; and these two names—the human spirit and the rational soul—designate one thing. This spirit, which in the terminology of the philosophers is the rational soul, embraces all beings, and as far as human ability permits discovers the realities of things and becomes cognizant of their peculiarities and effects, and of the qualities and properties of beings. But the human spirit, unless assisted by the spirit of faith, does not become acquainted with the divine secrets and the heavenly realities. It is like a mirror which, although clear, polished, and brilliant, is still in need of light. Until a ray of the sun reflects upon it, it cannot discover the heavenly secrets.

But the mind is the power of the human spirit. Spirit is the lamp; mind is the light which shines from the lamp. Spirit is the tree, and the mind is the fruit. Mind is the perfection of the spirit, and is its essential quality, as the sun’s rays are the essential necessity of the sun. 

- ‘Abdu’l-Baha  (‘The Baha’i World Faith’)

“…spirit in general is divided into five sorts—the vegetable spirit, the animal spirit, the human spirit, the spirit of faith, and the divine spirit of sanctity.”

Now as to what thou askest concerning the spirit and its “return” to this world of humanity and this elemental space: Know that spirit in general is divided into five sorts—the vegetable spirit, the animal spirit, the human spirit, the spirit of faith, and the divine spirit of sanctity.

The vegetable spirit is the virtue augmentative, or growing or vegetative faculty, which results from the admixture of the simple elements, with the co-operation of water, air and heat.

The animal spirit is the virtue perceptive resulting from the admixture and absorption of the vital elements generated in the heart, which apprehend sense impressions.

The human spirit consists of the rational, or logical, reasoning faculty, which apprehends general ideas and things intelligible and perceptible.

Now these “spirits” are not reckoned as Spirit in the terminology of the Scriptures and the usage of the people of the Truth, inasmuch as the laws governing them are as the laws which govern all phenomenal being (i.e., all existences belonging to the phenomenal or material universe, called “the world of generation and corruption”), in respect to generation, corruption, production, change and reversion, as is clearly indicated in the Gospel where it says: “Let the dead bury their dead;” “That which is born of the flesh is flesh, and that which is born of the Spirit is Spirit”; inasmuch as he who would bury these dead was alive with the vegetative, animal and rational human soul, yet did Christ—to whom be glory! — declare such dead and devoid of life, in that this person was devoid of the Spirit of Faith, which is of the Kingdom of God. 

- ‘Abdu’l-Baha  (‘Tablets of ‘Abdu’l-Baha’, vol. 1)