Allah the mighty and sublime said in the quran ;
Indeed in that are signs for those who discern [15:75]
and our beloved prophet Muhammad (PBUH) said ;
Abu Sa'id al-Khudri reported: The Messenger of Allah, peace be upon him, said, "Beware of the intuition of the believer. Verily, he sees with the light of Allah." Then, the Prophet recited the verse, "Verily, in that are signs for those of discernment." [sunan Al-Tirmidhi]
the fifth word of verse (15:75) is mutawassimeen (translated to discern in english), regarding this word the greatest interpreter of quran said ;
Abdullah Ibn Abbas (RA) said that it means "those who watch closely."
another great scholar said ;
Ibn al-Qayyim said, "It is a light that Allah bestows in the heart of his servant, by which he distinguishes between truth and falsehood, advantage and disadvantage, the honest and the liar." [Madarij al-Salikin 2/453]
spiritual experiences are possible in islam but not in the level of miracles as miracles in its true sense are only given to prophets and messengers. and every spiritual experience does not have to be something which manifests outward. as it is something a person experiences to himself the only other witness will be his creator in most of the times.
WHAT IS A SPIRITUAL EXPERIENCE (opinion based)
what exactly is a spiritual experience and how can it be defined. does the great feeling you have after you have performed a prayer with all the kushoo can be a spiritual experience?. or does the change in your behavior for good after rigorous worship in the month of fasting considered a spiritual experience?. or the feeling you have when you see kaaba'a (masjid al-haram) for the first time?, or the rejuvenated feeling of spending the desired time on the arafat plains on Hajj?. or do we consider those times when the feeling of tranquility over takes us when we recite quran as spiritual experience?. OR are we to consider the creator Himself calling us or sending angels in their true form to us as the only spiritual experinces?. subahaanallah!
in islam, these spiritual experiences are to be felt within. it is only for the person and there is no relevant need to disclose it. it is a form of guidance from Allah azzawajjal. one simple way that i understand is that if such an experience doesn't change anything in your life for good, then it's a 'mind trick'. such acts can be most probably from our greatest enemy, Iblis.(satan)
when you go applying science to everything in religion there will come a point that science will fall behind and that's when they will brand you as hallucinating, bogus and finally define you with mental illness. science does not have a valid explanation for the unseen, what goes beyond their electron microscope just simply dosen't exist for them. thus spiritual experiences cannot be defined by science nor should we try to find reason with science for it. it's just, science is handicapped when it comes to spiritual realms and dimensions. (they might try using the word quantum to explain it all but in the end ot won't make sense)
SPIRITUAL EXPERIENCE AND KARAMAH (lit. generosity, high-mindedness)
KARAMAH can be considered as the highest form of spiritual experience outward, as it can be witnessed by others.
karamah is what Allah shows at the hands of a pious, to whom Allah hath paved the path to guidance, goodness, piety, and faith, and avoided him misguidance, disobedience, and heresy, and have guided him of his religious affairs. there are many instances of this in the Quran and the Sunnah, as well as narrations about some righteous people.
[see al-Qasas verses 7-9, al-Kahf verses 8-15 and 65-78, al-Naml
verses 38-40, Aal ‘Imran verse 37, and Maryam verse 25.]
SPIRITUAL EXPRIENCE AND FIRASAH
FIRASAH can be considered as the highest form of spiritual experience inward, as it is something harldy witnessed by others than the person who experiences it.
spiritual insight, or firasah, is a faith-based insight that Allah azzawajjal casts into the hearts of His faithful ones, by which peoples' states or deeds are unveiled to them.
note : In his magesterial Madarij al-Salikin, Ibn Qayyim al-Jawziyyah discusses the reality of firasah, its cause, the sayings of the early masters concerning it, and its types. He also relates some wondrous accounts about the firasah of his shaykh and mentor, Shaykh al-Islam Ibn Taymiyyah.
for a muslim everything has to be spiritual, no matter what he does. in islam we have guidelines for everything. how to live and even how to die. every act is a experience so generally speaking, for a true muslim everything is a spiritual experience. i say this because Allah azzawajjal said in quran ;
They made not a just estimate of Allah such as is due to Him.[39:67]
may Allah the mighty and sublime grant us mercy and guide us to the straight path.
ALLAH KNOWS BEST
Tafsir of quran by Ibn Kathir
Al-Fawa'id (Makkah: Dar 'Alam al-Fawa'id, 2008)
Madarij al-Salikin (Riyadh: Dat Taybah, 2008)