Background A high prevalence of non-dipping diastolic blood pressure (DBP) patterns has been observed in Obstructive Sleep Apnea (OSA), suggesting that diminished circadian blood pressure variability may significantly contribute to hypertensive end-organ damage. Objectives This study aimed to evaluate cardiovascular complications in non-dipper OSA patients using a combination of 24-hour Ambulatory Blood Pressure Monitoring (ABPM), Holter electrocardiography, and transthoracic echocardiography (TTE). Methods This cross-sectional study assessed 64 adult non-dipper OSA patients. The patients, with an average age of 46.5 years, underwent clinical assessments via sphygmomanometer, resting electrocardiogram (ECG), TTE, 24-hour ABPM, and 24-hour Holter ECG. The average age of the patients was 46.5 years, with 50% exhibiting grade 2 obesity. OSA severity was classified as follows: 42.2% moderate; 32.8% severe; and 25% mild. A positive correlation was identified between OSA severity and body mass index (BMI), diabetes, and hypertension. ABPM revealed masked hypertension in 45% of participants. TTE showed that severe OSA was linked to regional wall motion abnormalities, ischemic changes, and increased interventricular septal thickness. Elevated pulmonary artery systolic pressure is predominantly observed in patients with severe OSA. Holter monitoring detected intermittent atrial fibrillation in 15.6% and infrequent extrasystoles in 31.2%. The multivariate logistic regression analysis identified BMI, age, male gender, and the presence of hypertension and diabetes mellitus as significant risk factors for severe OSA. Higher BMI, age, male gender, and these comorbidities increased the likelihood of severe OSA, with odds ratios of 1.22, 1.03, 2.80, and 1.85, respectively. Conclusions The 24-hour ABPM is an effective tool for detecting masked hypertension in non-dipper OSA patients. Additionally, the severity is directly associated with an increased risk of cardiovascular disease (CVD). Regular cardiovascular assessments are recommended for patients with OSA to mitigate potential complications.