Thanks for the query to HCM.
History of illness is very ambiguous so very difficult to answer but lightheadedness
may be due to .
1 Anemia , diagnosis can be confirmed by hemoglobin
2 In few persons urge of defecation causes mild increase in blood pressure so that may be the reason .
3 Amoebic colitis is the another reason so get in stool examination enamoeba histolica .
4 Ulcer in very early stage may be in colon .Diagnosis can be confirmed by colonoscopy
In my opinion deal as mentioned above.