How can you prevent unwanted acute disease after a constitutional remedy?

[Homeopathim]

Hi,

As a constitutional remedy, a parson took Silica 30c.

After a few hours he started having a severe sore throat and that developed to a coryza, coughing and expectoration.

All that passed yesterday - after 2 weeks.

Now he wants to continue with the Silica 30c, but he is afraid to take it from fear that he will get again the same acute disease that he previously just had.

Is it possible that he will be ill acutely again after Silica? How can he avoid this risk and still take the Silica?

Many thanks for your helpful reply.

Rafy