It is definite that a mantra helps to create specific brain-waves. These waves stimulate the corresponding glands and as a result they release the respective hormones. Therefore, keeping your physical and emotional health into consideration before initiating you into tantra with a beej-mantra, is very important rather Essential.
We can understand it by an example; that, if a person has an issue with his eyes (for example glaucoma, or retinal issues) and if he gets initiated by some unskilled Guru (or so called Mentor), into a mantra (or a beej mantra) which stimulates petals of higher chakras, it is likely that the intra-ocular pressure could increase which could exaggerate the problem for the disciple or the shishya!
Similarly, if a person has some issues with his heart (hypertension/post cardiac procedure, etc) and without taking into consideration this medical condition if he gets Mantra Deeksha by some amateurish Mentor into a mantra which has heavy base-sound of the Anahat (Heart) chakra, it could affect his health adversely, not to talk of the intended benefits!
Please be advised to take mantra-energy seriously and do not choose to do recitation of beej-mantras without consulting an able Guru.