Selection of right potency of a particular medicine is important for the cure of the a disease and such prescription of medicines in an appropriate potency reflects the experience of the Homoeopathic Doctor. However, a general trend has been observed that in an acute disease low potency of Homoeopathic medicine such as 30C, 200C are administered and for the chronic diseases, it is preferred to go in for higher potencies such as 1M, 10M, CM etc for the complete cure of the diseases. Doses are chosen by the Homoeopathic - doctors by keeping a close watch of the patients followed by painstaking query of different parameters such as ones' food - habit, sleeping pattern, regular motion details, ones' liking or disliking, time of aggravation of the diseases etc. Taking all parameters into account, appropriate medicine is selected for the patient and so a high degree of prudence is involved in judgement of Homoeopathic - medicine.
Aggravation may take place in administration of higher potency of Homoeopathic - medicine such as 1M, 10M, CM etc. Aggravation means that a right medicine has been selected for the disease and stoping medicine for the time being so as to allow the previous medicine to react vigorously with the system of the body is done deliberately. Aggravation is temporary and the end - result is quite amazing- a permanent cure of the prevailing disease.
Again, it is not necessary that higher the potency of the medicine, higher the aggravation. Even the high potency of Lycopodium of CM potency may not cause aggravation but if Sulphur of 200 potency, though considered a medium powered potency may result in tremendous aggravation.
In general, low potencies medicines like 3C, 6C, 30C don't cause aggravation and are safe to be used.
In regard to your last query, such manifestations are remote.