Recently, I did Istikhara regarding an issue, and had a dream. How do I know whether or not this dream is from Allah, or it is just a reflection of my mind.

The answer to an Istikhara is not necessarily in the form of a dream. It may
also be in the form of a feeling in the heart . Upon making Istikhara if one
is content, then it is a positive sign. If you have seen a dream and did not
understand its meaning, then you should refer to a person who is able to
interpret the drean for you. We furhter advise that in making decisions you
should also make mashwara(consultation) with reliable people.

And Allah Ta'ala knows best

Mufti E. Desai