How does this interact with Parkinson's and the following medication list?

This is from the drugs.com interaction checker:

"Drug Interaction Results

carbidopa (Ingredient of Sinemet)
gabapentin
hydrochlorothiazide
Klor-Con (potassium chloride)
levodopa (Ingredient of Sinemet)
mirtazapine
Uroxatral (alfuzosin)

Interactions between your selected drugs
hydrochlorothiazide and levodopa (Ingredient of Sinemet) (Moderate Drug-Drug)

MONITOR: The hypotensive effects of levodopa and antihypertensive agents may be additive. Postural hypotension may occur.

MANAGEMENT: Hemodynamic responses should be monitored during coadministration, especially during the first few weeks of therapy. Dose adjustments of the antihypertensive agent may be required. Patients should be advised to notify their physician if they experience dizziness or syncope.

hydrochlorothiazide and mirtazapine (Moderate Drug-Drug)

MONITOR: Many psychotherapeutic and CNS-active agents (e.g., anxiolytics, sedatives, hypnotics, antidepressants, antipsychotics, opioids, alcohol, muscle relaxants) exhibit hypotensive effects, especially during initiation of therapy and dose escalation. Coadministration with antihypertensive agents, in particular vasodilators and alpha-blockers, may result in additive effects on blood pressure and orthostasis.

MANAGEMENT: Caution is advised during coadministration of these agents. Close monitoring for development of hypotension is recommended. Patients should be advised to avoid rising abruptly from a sitting or recumbent position and to notify their physician if they experience dizziness, lightheadedness, syncope, orthostasis, or tachycardia.

hydrochlorothiazide and Uroxatral (alfuzosin) (Moderate Drug-Drug)

MONITOR: The hypotensive effects of thiazide diuretics and alpha-adrenergic blockers may be additive. Postural hypotension may occur.

MANAGEMENT: Hemodynamic responses should be monitored during coadministration, especially during the first few weeks of therapy. Patients should be advised to take the alpha-blocker at bedtime and to notify their physician if they experience dizziness or syncope while awake.

levodopa (Ingredient of Sinemet) and Uroxatral (alfuzosin) (Moderate Drug-Drug)

MONITOR: The hypotensive effects of levodopa and antihypertensive agents may be additive. Postural hypotension may occur.

MANAGEMENT: Hemodynamic responses should be monitored during coadministration, especially during the first few weeks of therapy. Dose adjustments of the antihypertensive agent may be required. Patients should be advised to notify their physician if they experience dizziness or syncope.

gabapentin and mirtazapine (Moderate Drug-Drug)

MONITOR: Central nervous system- and/or respiratory-depressant effects may be additively or synergistically increased in patients taking multiple drugs that cause these effects, especially in elderly or debilitated patients.

MANAGEMENT: During concomitant use of these drugs, patients should be monitored for potentially excessive or prolonged CNS and respiratory depression. Ambulatory patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

mirtazapine and Uroxatral (alfuzosin) (Moderate Drug-Drug)

MONITOR: Many psychotherapeutic and CNS-active agents (e.g., anxiolytics, sedatives, hypnotics, antidepressants, antipsychotics, opioids, alcohol, muscle relaxants) exhibit hypotensive effects, especially during initiation of therapy and dose escalation. Coadministration with antihypertensive agents, in particular vasodilators and alpha-blockers, may result in additive effects on blood pressure and orthostasis.

MANAGEMENT: Caution is advised during coadministration of these agents. Close monitoring for development of hypotension is recommended. Patients should be advised to avoid rising abruptly from a sitting or recumbent position and to notify their physician if they experience dizziness, lightheadedness, syncope, orthostasis, or tachycardia."

Your doctor should be aware of these potential drug interactions - increased light headedness and dizziness and increased blood-pressure are the main potential problems with these drugs been taken together.