Number of class of warrant or right cancelled during the period.

No definition available.

Name:	hsdt_ClassOfWarrantOrRightCancelled
Namespace Prefix:	hsdt_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Class of warrant or right exercised.

+ References

No definition available.

+ Details

Name:	hsdt_ClassOfWarrantOrRightExercised
Namespace Prefix:	hsdt_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Derivative warrant liability reclassified to equity on exercise of warrants.

+ References

No definition available.

+ Details

Name:	hsdt_DerivativeWarrantLiabilityReclassifiedToEquityOnExerciseOfWarrants
Namespace Prefix:	hsdt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of net proceeds receivable from holders exercising their stock warrants.

+ References

No definition available.

+ Details

Name:	hsdt_NetProceedsReceivableFromWarrantExercises
Namespace Prefix:	hsdt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of volume weighted average price days post reverse stock split for warrant exercise price reset.

+ References

No definition available.

+ Details

Name:	hsdt_WarrantsExercisePriceResetNumberOfDaysVolumeWeightedAveragePrice
Namespace Prefix:	hsdt_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Exercise price per share or per unit of warrants or rights outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-3

+ Details

Name:	us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ClassOfWarrantOrRightLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

+ References

+ Details

Name:	us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of warrants or rights outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_ClassOfWarrantOrRightOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483466/210-20-50-3

+ Details

Name:	us-gaap_DerivativeLiabilitiesNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Period between issuance and expiration of outstanding warrant and right embodying unconditional obligation requiring redemption by transferring asset at specified or determinable date or upon event certain to occur, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

+ Details

Name:	us-gaap_WarrantsAndRightsOutstandingTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ClassOfWarrantOrRightAxis=hsdt_Warrants2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ClassOfWarrantOrRightAxis=hsdt_CommonStockWarrantsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ClassOfWarrantOrRightAxis=hsdt_PreFundedWarrantsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

COMMON STOCK, PREFERRED STOCK AND WARRANTS - Warrants (Details) - USD ($) $ / shares in Units, $ in Thousands		6 Months Ended
	May 09, 2024	Jun. 30, 2024	Dec. 31, 2023	Aug. 09, 2022
Warrant activity
Fair value of derivative liability		$ 347	$ 3,323
Derivative warrant liability reclassified to equity on exercise of warrants		$ 101
Weighted Average
Warrant activity
Exercise price		$ 3.65
2022 Warrants
Warrant activity
Fair value of derivative liability		$ 300	$ 3,300
Number of warrants outstanding		603,690
Exercise price	$ 1.6163	$ 6.9135
Shares of common stock purchasable with warrants				720,000
Number of days, warrants exercise price reset	5 days	5 days
Warrant expiration period		5 years
Number of warrants exercised		23,400
Number of warrants cancelled		0
Net proceeds of warrant exercise amount		$ 162
Equity-classified Warrants
Warrant activity
Number of warrants outstanding		6,399,466
Number of warrants exercised		1,604,778
Equity-classified Warrants \| Weighted Average
Warrant activity
Exercise price		$ 3.34
Pre-funded Warrants
Warrant activity
Number of warrants outstanding		542,444
Exercise price		$ 0.001